Method for purifying matter contaminated with halogenated organic compounds

ABSTRACT

A method for purifying matter contaminated with a halogenated organic compound is disclosed. The method includes the step of adding a reducing agent and a nutritional source for a heterotrophic anaerobic microorganism to the contaminated matter. The reducing agent is reduced iron, cast iron, iron-silicon alloy and so on, or a water soluble compound. A combination of chemical reactions with microorganisms allows to decompose the halogenated organic compound. The nutritional source including an organic carbon and 20 to 50 percent by weight of an oxidized form of nitrogen is added, thereby preventing by products of the decomposition such as generation of noxious gases and decoloration of soil. A method includes the steps of mixing a reducing agent and a nutritional liquid with the contaminated matter, wherein the mixing step including a step of adjusting the contaminated matter at pH ranging from 4.5 to 9.0; and keeping the mixture in a condition that air hardly penetrates through a matrix, thereby allowing to uniformly mix a large amount of the contaminated matter.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for purifying mattersuch as soil, sediment, sludge and water contaminated with halogenatedorganic compounds, particularly a chlorinated organic compound. Thepresent invention particularly relates to a method for purifyingcontaminated matter by reductive dehalogenation combining a chemicalreaction with a biological reaction, thereby decomposing the halogenatedorganic compound.

RELATED ART

[0002] Recently, halogenated organic compounds such astetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane, anddichloroethylene are wide used as a degreasing agent for electroniccomponents and mechanical metal components and a cleaning agent for drycleaning. Halogenated organic compounds are contaminants in soil andground water. These halogenated organic compounds do not readilydecompose in the natural world and are hardly soluble in water, andtherefore tend to accumulate in soil and to penetrate into ground water.Moreover, halogenated organic compounds are known to induce hepaticdisorders and cancer. Therefore, it is desirable to decomposehalogenated organic compounds such as chlorinated organic compounds insoil and so on.

[0003] In these days, bioremediation has been receiving attention topurify soil, ground water and so on contaminated with halogenatedorganic compounds. Bioremediation is safe and has improved costs toeffects. However, the bioremediation requires a long period of time tobe effective and there are limits on the kinds and concentrations ofsubstances that can be decomposed. Therefore, we may not necessarily besatisfied with the bioremediation

[0004] The bioremediation includes aerobic decomposition oftrichloroethylene with methane assimilating microorganism,toluene/phenol decomposing microorganism, ammonia oxidizingmicroorganism and alkene assimilating microorganism, and there arenumerous reports on the aerobic decomposition. However, the aerobicdecomposition has disadvantages as follows: decomposition reactions areunstable; the range of substances able to be decomposed is very limited;and highly chlorinated compounds such as tetrachloroethylene and carbontetrachloride cannot be decomposed.

[0005] On the other hand, many anaerobic microorganisms have specificityto decompose a wide range of highly chlorinated compounds such astetrachloroethylene, trichloroethylene, carbon tetrachloride and so on.However, the anaerobic microorganisms have disadvantages in that growththereof is very slow; and anaerobic microorganisms produce and thusaccumulate strongly toxic intermediate metabolites in the process of theanaerobic decomposition (see H. Uchiyama and S. Yagi; Bioscience andindustry, Vol. 52, No. 11, pp. 879-884, 1994).

[0006] On the other hand, it has been reported that halogenated organiccompounds can be decomposed by chemical reactions, and reductivetreatment of chlorinated organic compounds with metallic iron has beendisclosed (see T. Senzaki; Treatment of Ground Water Contaminated withChlorinated Organic Compounds—treatment technique with activated carboncarrying metal iron at low temperatures; “PPM” Vol. 26, No. 5, pp.64-70, 1995). In view of the foregoing, the present inventors trieddechlorination tests wherein metallic iron is added to soil in theabsence of a carbon source for a microorganism. However, underconditions that microorganism is not cultivated and particularlyconditions that a reductive atmosphere and a neutral condition are notmaintained, the present inventors did not observe any dechlorinationreaction. Moreover, the addition of an iron salt such as FeCl₂, FeCl₃and FeSO₄ instead of the metallic iron did not produce thedechlorination reaction, either.

[0007] It has been reported that metallic iron and high-pressure air canbe injected into soil for reacting iron powder with halogenated organiccompounds in the soil to convert into inorganic compounds, therebydetoxifying the same (see Japanese Patent Application Laid Open No.8-257570). However, the method has disadvantages concerning equipmentfor injecting air and there is a chance that the halogenated organiccompounds may diffuse. Moreover, the use of high-pressure air increasescosts, and therefore is not practical.

[0008] It has been reported that chlorinated organic compoundscontaminating soil and ground water can be removed by combining anatural compound having catalytic activity for dehalogenation withmicroorganism treatment (see “Nikkei Biotech” published by Nikkei BPInc., Oct. 7, 1996, No. 361, pp. 14-15). However, the document does notdisclose specific natural compounds and the microorganism at all.

[0009] U.S. Pat. No. 5,411,664 discloses a method for decomposinghalogenated organic compounds by adding fibrous organic matter andmultivalent metal particles to a contaminated matter. However, the U.S.patent does not disclose a reducing agent such as reduced iron, castiron, alloy, a water soluble reducing agent and so on. Moreover, theU.S. patent does not disclose maintaining the contaminated matter in areductive atmosphere or a specific pH subsequent to adding the reducingagent.

[0010] Moreover, depending on the composition of a nutritional sourceadded, biological reductive reactions such as sulfate reduction andmethane fermentation may occur, and sulfur-containing noxious gases suchas hydrogen sulfide and mercaptan are produced and a combustible gassuch as a methane gas may be generated. Moreover, the production of ironsulfide may change color of soil into black. A reaction of metallicpowder and water may produce a combustible hydrogen gas.

[0011] In a laboratory scale, it is easy to homogeneously mix a reducingagent and a nutritional source with a contaminated matter. However, inorder to purify contaminated matter such as soil, in reality, a largeamount of reducing agent and the nutritional source would be required,which may warrant engineering works. Moreover, it is not easy tohomogeneously mix the contaminated matter in such a large scale.Furthermore, it is expected that mixing conditions may affect adecomposition rate of halogenated organic compounds. Particularly, aspecial technique is required to purify the contaminated matter having avolume of not less than 1 m³ and particularly not less than 10 m³.

SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to provide a method forpurifying matter contaminated with a halogenated organic compound bycombining chemical reaction with a biological reaction, therebydecomposing the halogenated organic compound.

[0013] The first aspect of the present invention has an object ofdecomposing the halogenated organic compounds by reductivedehalogenation reaction.

[0014] The second aspect of the present invention has an object ofdecomposing the halogenated organic compounds by a chemicaldehalogenation reaction.

[0015] The third aspect of the present invention has an object ofpreventing the generation of sulfur-containing noxious gas andcombustible gas as well as the excessive decoloration of contaminatedmatter such as soil, which may occur as a result of by-products of thereductive dehalogenation reaction.

[0016] The fourth aspect of the present invention has an object ofmixing the reducing agent and the nutritional source with thecontaminated matter when the contaminated matter has a large volume.

[0017] The first aspect of the present invention is characterized byadding a prescribed reducing agent, thereby promoting the reductivedehalogenation reaction.

[0018] The second aspect of the present invention is characterized byadding a prescribed reducing agent, thereby promoting the chemicalreductive dehalogenation reaction. Contrary to the first aspect of thepresent invention, the second aspect need not involve the use of abiological reaction. Use of the prescribed reducing agent allows todecompose halogenated organic compounds solely by chemical reactions.

[0019] In the third aspect of the present invention, a nutritionalsource containing an organic carbon and 20 to 50 percent by weight,based on the organic carbon, of an oxidized form of nitrogen is used soas to change a group of microorganisms involved in reductivedehalogenation reaction, thereby preventing soil from being changed incolor to black and noxious gases such as mercaptan from being generated.

[0020] The fourth aspect of the present invention is achieved by mixinga reducing agent and a nutritional liquid with a contaminated matter,thereby uniformly mixing thereof, especially when the contaminatedmatter having a volume of not less than 1 m³ and particularly not lessthan 10 m³ is purified.

[0021] In the third and fourth aspects of the present invention, thereducing agent used in the first and second aspects of the presentinvention is preferably used but not limited thereto.

[0022] According to the first aspect of the present invention, there isprovided a method for purifying matter contaminated with a halogenatedorganic compound, which method comprises the steps of: adding a reducingagent and a nutritional source for a heterotrophic anaerobicmicroorganism to the contaminated matter, the reducing agent having astandard electrode potential ranging from 130 mV to −2400 mV at 25° C.with respect to the standard hydrogen electrode, the reducing agent isat least one species selected from the group consisting of reduced iron,cast iron, iron-silicon alloy, titanium alloy, zinc alloy, manganesealloy, aluminum alloy, magnesium alloy, calcium alloy and a watersoluble compound. The presence of such reducing agent promotes reductivedehalogenation reaction by combination of chemical reactions andmicroorganisms.

[0023] In the present invention, preferably, the reducing agent has thestandard electrode potential ranging from −400 mV to −2400 mV at 25° C.with respect to the standard hydrogen electrode, and the reducing agentis at least one species selected from the group consisting of thereduced iron, the cast iron, the iron-silicon alloy, the titanium alloy,the zinc alloy, the manganese alloy, the aluminum alloy, the magnesiumalloy, and the calcium alloy. Preferably, the reducing agent comprisesthe reduced iron. Alternatively, the reducing agent may comprise thecast iron. Alternatively, the reducing agent may be selected from thegroup consisting of the iron-silicon alloy, titanium-silicon alloy,titanium-aluminum alloy, zinc-aluminum alloy, manganese-magnesium alloy,aluminum-zinc-calcium alloy, aluminum-tin alloy, aluminum-silicon alloy,magnesium-manganese alloy and calcium-silicon alloy.

[0024] Preferably, the reducing agent is a water soluble compound.Further preferably, the reducing agent is an organic acid or derivativethereof, hypophosphorous acid or derivative thereof, or a sulfide salt.

[0025] Preferably, the reducing agent is a powder having a diameter upto 500 μm. Preferably, the contaminated matter has a water content of atleast 25 percent by weight.

[0026] Preferably, the method further comprises the step of maintainingthe contaminated matter in a pH ranging from 4.5 to 9.0 subsequent tothe adding step. Preferably, further comprising the step of maintainingthe contaminated matter in a pH ranging from 4.5 to 9.0 under a reducingatmosphere subsequent to the adding step.

[0027] Preferably, the method further comprises the steps of adding anorganic compost, a compostable organic material, a waste watercontaining organic matter or a waste containing organic matter to thecontaminated matter and mixing thereof.

[0028] In the first aspect of the present invention, preferably, thewater soluble reducing agent is monocarboxylic acid, dicarboxylic acid,tricarboxylic acid, tetracarboxylic acid or salt thereof, which may have1 to 20 carbon atoms, and which may be substituted by a hydroxy radical;polyhydroxyaryl; or hypophosphorous acid or salt thereof. Preferably,the water soluble reducing agent is hypophosphorous acid or saltthereof. The reducing agent may be a salt made of the organic acid orthe hypophosphorous acid and iron, titanium, zinc, manganese, aluminum,or magnesium.

[0029] Preferably, the method further comprises the step of adding atleast one of an alkali metal compound and an alkaline earth metalcompound to the contaminated matter for adjusting pH thereof. In themaintenance step, preferably, the halogenated organic compound isconverted into an organic compound being free of a halogen atom. In themaintenance step, preferably, the halogenated organic compound isconverted into a hydrocarbon being free of a halogen atom.

[0030] According to the second aspect of the present invention, there isprovided a method for purifying matter contaminated with a halogenatedorganic compound, which method comprises the step of: adding a reducingagent to the contaminated matter, the reducing agent having a standardelectrode potential ranging from 130 mV to −2400 mV at 25° C. withrespect to the standard hydrogen electrode, the reducing agent is atleast one species selected from the group consisting of reduced iron,cast iron, iron-silicon alloy, titanium alloy, zinc alloy, manganesealloy, aluminum alloy, magnesium alloy, calcium alloy and a watersoluble compound.

[0031] In the second aspect of the present invention, preferably, thereducing agent has the standard electrode potential ranging from −445 mVto −2400 mV at 25° C. with respect to the standard hydrogen electrode,and the reducing agent is at least one species selected from the groupconsisting of the iron-silicon alloy, the titanium alloy, the zincalloy, the manganese alloy, the aluminum alloy, the magnesium alloy, andthe calcium alloy.

[0032] Preferably, the contaminated matter comprises 0.1 g to 100 g ofan iron compound based on 1 kg of a dry weight of the contaminatedmatter. Further preferably, the contaminated matter comprises 1 g to 100g of an iron compound based on 1 kg of a dry weight of the contaminatedmatter, and the iron compound comprises iron hydroxide (Fe(OH)₃) ortriiron tetraoxide (Fe₃O₄). Preferably, the reducing agent is at leastone species selected from the group consisting of the iron-siliconalloy, titanium-silicon alloy, titanium-aluminum alloy, zinc-aluminumalloy, manganese-magnesium alloy, aluminum-zinc-calcium alloy,aluminum-tin alloy, aluminum-silicon alloy, magnesium-manganese alloyand calcium-silicon alloy.

[0033] Alternatively, the reducing agent preferably may be a watersoluble compound. Preferably, the reducing agent is an organic acid orderivative thereof, hypophosphorous acid or derivative thereof, or asulfide salt. Preferably, the reducing agent is a powder having adiameter up to 500 μm.

[0034] According to the third aspect of the present invention, there isprovided a method for purifying matter contaminated with a halogenatedorganic compound, which method comprises the step of: adding a reducingagent and a nutritional source for a heterotrophic anaerobicmicroorganism to the contaminated matter, the reducing agent having astandard electrode potential ranging from 130 mV to −2400 mV at 25° C.with respect to the standard hydrogen electrode, the nutritional sourcecontaining an organic carbon and 20 to 50 percent by weight, based onthe organic carbon, of an oxidized form of nitrogen.

[0035] Preferably, the nutritional source contains 20 to 30 percent byweight, based on the organic carbon, of the oxidized form of nitrogen.Preferably, the organic carbon is supplied as a water soluble organiccarbon source.

[0036] Preferably, the reducing agent is a metal having a standardelectrode potential ranging from −400 mV to −2400 mV at 25° C. withrespect to the standard hydrogen electrode. Preferably, the reducingagent is at least one species selected from the group consisting ofreduced iron, cast iron, iron-silicon alloy, titanium alloy, zinc alloy,manganese alloy, aluminum alloy, magnesium alloy, and calcium alloy.

[0037] Preferably, the reducing agent is a water soluble compound.Preferably, the reducing agent is a powder having a diameter up to 500μm.

[0038] In the third aspect of the present invention, preferably, theoxidized form of nitrogen is in a form of a nitrate salt. Preferably,the nitrate salt contains alkali metal nitrate, alkaline earth metalnitrate, iron nitrate, titanium nitrate, zinc nitrate, manganesenitrate, aluminum nitrate or magnesium nitrate. Further preferably, thenitrate salt contains sodium nitrate, potassium nitrate or calciumnitrate.

[0039] Preferably, the organic carbon source is a sugar, an organic acidor derivative thereof, lower alcohol, a morasses waste, a liquor wasteor a mixture thereof.

[0040] According to the fourth aspect of the present invention, there isprovided a method of purifying a contaminated matter containing ahalogenated compound and a solid matter, which method comprises the stepof: mixing a reducing agent and a nutritional liquid containing anutritional source for a heterotrophic anaerobic microorganism and waterwith the contaminated matter, the reducing agent having a standardelectrode potential ranging from 130 mV to −2400 mV at 25° C. withrespect to the standard hydrogen electrode, wherein the mixing stepincluding a step of adjusting the contaminated matter at pH ranging from4.5 to 9.0; and keeping the mixture in a condition that air hardlypenetrates through a matrix.

[0041] In the present invention, preferably, the reducing agent may bein a powder form and wherein the nutritional liquid is added to thecontaminated matter and mixed thereof, and then the reducing agent isadded to the resultant mixture and further mixed thereof.

[0042] Preferably, the reducing agent is a powder having a diameter upto 500 μm.

[0043] Preferably, the reducing agent is at least one species selectedfrom the group consisting of reduced iron, cast iron, iron-siliconalloy, titanium alloy, zinc alloy, manganese alloy, aluminum alloy,magnesium alloy and calcium alloy.

[0044] Preferably, 1 to 10 percent by volume, based on the contaminatedmatter, of the nutritional liquid is added to the contaminated matterand mixed thereof as a first step; and then an amount larger than theamount of the first step of the nutritional liquid is added to thecontaminated matter and mixed thereof as a second step.

[0045] Alternatively, 1 to 5 percent by volume, based on thecontaminated matter, of the nutritional liquid may be added to thecontaminated matter and mixed thereof as a first step; the nutritionalliquid may be added to the contaminated matter and mixed thereof as asecond step wherein a sum of the nutritional liquids added in the firststep and the second step amounts 5 to 10 percent by volume, based on thecontaminated matter, of the contaminated liquid; and the nutritionalliquid is added to the contaminated matter and mixed thereof as a thirdstep wherein an amount of the nutritional liquid added in the third stepis more than an amount of the nutritional liquid added in either thefirst step or the second step.

[0046] Preferably, the reducing agent is a water soluble compound, andthe reducing agent is dissolved in the nutritional liquid. Preferably,in the keeping step the mixture is kept at a temperature ranging from17° C. to 60° C. for at least initial three days.

[0047] In the fourth aspect of the present invention, preferably, inoverall, 15 to 25 percent by volume, based on the contaminated matter,of the nutritional liquid is added to the contaminated matter.

[0048] Preferably, in the keeping step the mixture is kept at atemperature ranging from 17° C. to 60° C. for at least initial fivedays. Further preferably, in the keeping step the mixture is kept at atemperature ranging from 20° C. to 40° C. for at least initial three,preferably five days.

[0049] Preferably, the keeping step is conducted in a situation that themixture is separated from the environment. Preferably, the contaminatedmatter is covered by a material that does not penetrate air so as tomaintain a condition that air hardly penetrates through a matrix.Alternatively, the contaminated matter is immersed in an aqueous liquidso as maintain a condition that air hardly penetrates through a matrix.Preferably, the nutritional liquid, the reducing agent and thecontaminated matter are mixed in a container.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050]FIG. 1 is a graph to show a test result where a soil contaminatedby tetrachloroethylene is purified by reductive dehalogenation reactionusing a medium for producing methane producing microorganisms underanaerobic conditions in accordance with the present invention.

[0051]FIG. 2 is a graph to show a test result where a soil contaminatedby tetrachloroethylene is purified by dehalogenation reaction using amedium for producing sulfate reducing microorganisms under anaerobicconditions in accordance with the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

[0052] According to the first, second and third aspects of the presentinvention, matter contaminated with a halogenated organic compound ispurified. In the present specification, the halogen refers to fluorine,chlorine, bromine, and iodine. In the present invention, mattercontaminated with an organic compound containing a halogen atom can bepurified, and particularly matter contaminated with an organic compoundcontaining a chlorine atom and a bromine atom can be purified, and moreparticularly matter contaminated with an organic compound containing achlorine atom can be purified. A chlorinated organic compound is notlimited to an aliphatic compound such as tetrachloroethylene,trichloroethylene, 1,1,1-trichloroethane, dichloroethylene and so on butto include an aromatic compound such as pentachlorophenol.

[0053] According to the first, second, third, and fourth aspects of thepresent invention, contaminated matter such as soil, sediment and sludgemay be treated. Moreover, a compost, compostable organic matter, and awaste can be treated. According to the first, second and third aspectsof the present invention, an aqueous liquid such as groundwater, and awaste water may be treated. In this specification, the aqueous liquidincludes an aqueous solution, a suspension, an emulsion and a mixturethereof.

[0054] When the contaminated matter is soil, sediment, sludge and so on,the water content thereof is preferably at least 25 percent by weight,and further preferable from 40 to 60 percent by weight. Under theseconditions, air hardly penetrate through the soil, sediment, sludge andso on, thereby proliferating anaerobic microorganism, and thereforethese conditions are preferable. The water content thereof in percent isdefined as follows:${{Water}\quad {Content}} = {\frac{{weight}\quad {of}\quad {water}\quad {therein}}{\begin{matrix}{{total}\quad {weight}\quad {of}\quad {contaminated}\quad {matter}} \\{{containing}\quad {water}}\end{matrix}} \times 100}$

[0055] When the contaminated matter is water such as groundwater and awaste water, the water content is always at least 25 percent by weight.

[0056] According to the first aspect of the present invention, areducing agent having a standard electrode potential ranging from 130 mVto −2400 mV at 25° C. with respect to the standard hydrogen electrodeand a nutritional source for a heterotrophic anaerobic microorganism tothe contaminated matter are added to the aforementioned contaminatedmatter so as to accelerate both chemical reaction and biologicalreaction, thereby decomposing the halogenated organic compound.

[0057] A substance having a standard electrode potential larger than 130mV may not provide sufficient reducing power. On the other hand, asubstance having a standard electrode potential smaller than −2400 mV,for example, alkali metal such as metallic sodium and metallic potassiumhas too much reducing power, and may violently react with water toproduce a hydrogen gas. Therefore, such substance is very dangerous andnot preferable. Standard electrode potentials (E°) at 25° C. withrespect to the standard hydrogen electrode are shown in the followingtable.

[0058] Standard Electrode Potential (E°) at 25° C. with respect toStandard Hydrogen Electrode Electrode Reactions E° (mV) Ca²⁺ + 2e⁻

Ca −2865 Na⁺ + e⁻

Na −2714 Mg²⁺ + 2e⁻

Mg −2363 Al³⁺ + 3e⁻

Al −1662 Zn²⁺ + 2e⁻

Zn −763 Fe²⁺ + 2e⁻

Fe −440 Cd²⁺ + 2e⁻

Cd −403 Ni²⁺ + 2e⁻

Ni −250 Sn²⁺ + 2e⁻

Sn −136 Fe³⁺ + 3e⁻

Fe −36 2H⁺ + 2e⁻

H₂  0 ascorbic acid (pH7.0)  58

[0059] The standard electrode potential is equal to the standardpotential E° and is determined with respect to a hydrogen electrodeserving as a comparing electrode when all of the chemical speciesinvolved in a cell reaction are standard states such as pure solidstate, standard concentrations, standard pressures and so on. Thestandard electrode potential is calculated by a formula as follows:

E°=−ΔG°/nF

[0060] wherein

[0061] ΔG° refers to a change of a standard Gibbs free energy in thecell reaction;

[0062] n is the number of electrons involved in the reaction; and

[0063] F is the Faraday constant.

[0064] Usually, the potential for oxidation and reduction may beexpressed by a potential determined by a saturated silver chlorideelectrode serving as a comparing electrode. The potential for oxidationand reduction is smaller than the standard electrode using the standardhydrogen electrode serving as the comparing electrode by about 200 mV.

[0065] In the present invention, the reducing agent is at least onespecies selected from the group consisting of reduced iron, cast iron,iron-silicon alloy, titanium alloy, zinc alloy, manganese alloy,aluminum alloy, magnesium alloy, calcium alloy and a water solublecompound.

[0066] Preferably, the reducing agent is a metallic substance having thestandard electrode potential ranging from −400 mV to −2400 mV at 25° C.with respect to the standard hydrogen electrode.

[0067] In one embodiment of the present invention, the reduced iron isused as the reducing agent. Usually, surfaces of an iron powder isoxidized to form an oxidized coating. On the other hand, the reducediron has much less oxidized coating, is prone to oxidation, and hashigher reactivity.

[0068] The reduced iron refers to a species of metallic iron produced byreduction of an oxide, and the reduced iron is very fine powder and veryprone to oxidation (“Encyclopaedia of Chemistry” edited by Committee ofEditing Encyclopaedia of Chemistry, Kyoritsu Publishing Company).Typically, the reduced iron is reduced by a hydrogen gas at hightemperatures. Iron oxide may be reduced, but the oxide is not limited toiron oxide. The reduced iron may have an Fe content more than 90percent. For example, such reduced iron is available from Wako PureChemical Industries, Ltd.

[0069] According to another embodiment of the present invention, castiron is preferably used as the reducing agent. Cast iron is both safeand easy to treat. Moreover, cast iron allows a high rate ofpurification to be achieved. A shaved scrap from a cast iron product,that is, scrap cast iron is further preferable for use since scrap castiron can be recycled.

[0070] Generally, iron ore is reduced to produce a pig iron, andimpurities are removed from the pig iron to provide an iron material forfurther use in industry. An iron material having up to about 2 percentby weight of carbon concentration is called steel, and an iron materialhaving more than about 2 percent by weight of carbon concentration iscalled cast iron (“Science and Chemistry Dictionary”, the fourthedition, Iwanami Publishing House, 1987, page 411). Steel has superiormechanical strength, and processed in a variety of manufactures. Weinvestigated the use of shaved scrap steel in purifying mattercontaminated by a halogenated organic compound. However, oil is used inshaving, and therefore the shaved scrap from a steel product contains anoil. When such shaved scrap is used in purifying a contaminated matter,there is a chance that the oil might produce a secondary contamination.On the other hand, no oil is used during shaving cast iron used incasting, and therefore, cast iron scrap will not produce secondarycontamination, being contrary to the scrap of the steel product.

[0071] According to another aspect of the present invention, an alloy isused as the reducing agent. Specifically, an iron-silicon alloy, atitanium alloy, a zinc alloy, a manganese alloy, an aluminum alloy, amagnesium alloy, and a calcium alloy are used also. The titanium alloyincludes, for example, a titanium-silicon alloy and a titanium-aluminumalloy. The zinc alloy includes, for example, a zinc-aluminum alloy. Themanganese alloy includes, for example, a manganese-magnesium alloy. Thealuminum alloy includes, for example, an aluminum-zinc-calcium alloy, analuminum-tin alloy, an aluminum-silicon alloy. The magnesium alloyincludes, for example, a magnesium-manganese alloy. The calcium alloyincludes, for example, a calcium-silicon alloy.

[0072] Functions of the reducing agent are explained in the case of thereduced iron as an example. According to a report by Senzaki concerningan anaerobic dehalogenation by metallic a iron (“Treating GroundwaterContaminated by Organic Chlorinated Compound; Treatment Technique at LowTemperatures by Activated Carbon Carrying Metallic Iron” PPM, 1995, Vol.26, No. 5, pages 64 to 70), the halogenated organic compound is adsorbedonto a surface of the reduced iron, and surfaces of the reduced iron arepolarized to produce anodes and cathodes depending on conditions of themetal and the environment. Accordingly, iron dissolves into iron ions atthe anodes while electrons flow into cathodes so that reductivereactions such as dehalogenation reactions occur at the cathodes.

Anode: Fe→Fe²⁺+2e⁻

[0073] As aforementioned, the cast iron has more than 2 percent byweight of carbon concentration, and typically contains 3 to 3.5 percentby weight and 13 to 14 percent of carbon as graphite. The scrap castiron is generally pulverized by a mill prior to being discharged as awaste. During the pulverization, a part of the graphite is removed andadhere to a surface of a powder of the cast iron. Therefore, when thepowder of the cast iron is coated by a water film, the graphite mayserve as the cathode, and the iron may serve as the anode. As a result,an electric current may flow as aforementioned, and the iron maydissolve at the anode and a reduction reaction such as a dehalogenationreaction may occur at the cathode.

[0074] An alloy having a stronger reduction power than metallic ironmore easily maintains a reducing atmosphere, have increased potentialdifference from the halogenated organic compound, and accelerate thedehalogenation reaction.

[0075] Use of an alloy such as the magnesium-manganese alloy, thezinc-aluminum alloy, the aluminum-zinc-calcium alloy, the aluminum-tinalloy and so on, may not form an oxide coating or a corrosion productadhered onto the alloy surface. Although such coating is coated onto thesurface of the alloy, the coating is not dense or passivated and doesnot impede the dehalogenation reaction. Therefore, the reductionreaction does not decrease the contact efficiency, and the purificationreaction remains efficient.

[0076] According to another embodiment of the present invention,preferably, the reducing agent is a water soluble compound. Compared toadding a solid such as powder, the contact efficiency with thehalogenated organic compound significantly increases, therebyaccelerating the dehalogenation reaction. Moreover, the water solublereducing agent is capable of penetrating soils and so on, and thereducing agent can be injected through an injecting well so that diggingmay not be required. Furthermore, when reducing conditions becomeunstable during a purification operation, an exuded water from thecontaminated matter may be recovered, the water soluble reducing agentmay be added thereto, and then the mixture may be injected again,thereby easily recovering the reducing condition.

[0077] The water soluble reducing agent may include an organic acid orderivative thereof, hypophosphorous acid or derivative thereof, and asulfide salt. The organic acid includes carboxylic acid, sulfonic acid,phenol or derivative thereof. The carboxylic acid includesmonocarboxylic acid, dicarboxylic acid, tricarboxylic acid,tetracarboxylic acid or salt thereof, which may have 1 to 20 carbonatoms, and which may be substituted by a hydroxy radical. For example,the carboxylic acid includes formic acid, acetic acid, citric acid,oxalic acid, terephthalic acid, and so on, and an aliphatic dicarboxylicacid having 2 to 10 carbon atoms such as citric acid and oxalic acid areparticularly preferable.

[0078] As the phenol derivative, polyhydroxyaryl is preferable. Thepolyhydroxyaryl refers to aryl having a plurality of hydroxy groupssubstituted thereby, and aryl includes, for example, benzene,naphthalene, anthracene, and so on. Like naphthalene and indene, a fuzedring may be formed. As the polyhydroxyaryl, 1,2,3-trihydroxybenze,1,4-dihydroxybenzene are preferable. 1,2,3-trihydroxybenze is calledpryogallol or pyrogallic acid also. Its alkaline solution reacts with anoxygen gas to produce an oxide.

[0079] The derivative of the organic acid includes, for example, salt,ester, amide, anhydride and so on, and the salt is preferable. Thecounter ion is not limited and include an inorganic ion and an organicion such as tetraalkyl ammonium ion. The inorganic ion includes analkali metal ion such as sodium ion; an alkaline earth metal ion such ascalcium ion; and a transition metal ion such as iron ion, titanium ion.

[0080] The derivative of hypophosphorous acid includes, for example,salt, ester, and so on, and the salt is preferable. The counter ion isnot limited and include an inorganic ion and an organic ion such astetraalkyl ammonium ion. The inorganic ion includes an alkali metal ionsuch as sodium ion; an alkaline earth metal ion such as calcium ion; anda transition metal ion such as iron ion, titanium ion.

[0081] The reducing agent may be a salt made of the organic acid or thehypophosphorous acid and iron, titanium, zinc, manganese, aluminum, ormagnesium.

[0082] Addition of the aforementioned reducing agent does not produce oraccumulate an intermediate metabolite such as vinyl chloride, which wasreported in many of anaerobic dehalogenation reaction, and the reactionproducts are converted to a substance that is completely dehalogenatedand released to a gas phase. Use of a reducing agent having the standardelectrode potential being equal to or smaller than metallic ironincreases potential difference from the halogenated organic compound,thereby accelerating dehalogenation reaction. Therefore, its use ispreferable.

[0083] When the contaminated matter is soil, an amount of the reducingagent is preferably from 0.01 to 20 gram and further preferably from0.05 to 10 gram per 100 gram of the soil. When the contaminated matteris water, an amount of the reducing agent is preferably from 0.1 to 30gram and further preferably 0.2 to 20 gram per 100 milliliters of water.In either case, when the contaminated matter has a concentration of thehalogenated compound, which is an object of dehalogenation, more than 50milligram per kilogram or 50 milligram per liter, an amount of thereducing agent such as a metallic powder may be required to increase by0.05 to 0.1 gram per 1 milligram of the halogenated organic compound.However, these values apply in ideal conditions, and there are cases inan actual contaminated site where microorganisms do not consume oxygenas expected and thus the reducing power of the reducing agent isconsumed in vain. Moreover, the reducing power of the reducing agent canbe easily consumed by supply of water from rain and an oxygen gas inair. Therefore, in practicing the present invention, a preliminary teston site should be conducted, and concentrations of the reducing agentshould be determined, depending on conditions on the site.

[0084] Preferably, the reducing agent is in a form of powder or asolution for increasing contact efficiency of the reducing agent withthe contaminated matter. However, most of the aforementioned reducingagent may react with water to easily form an oxidized compound. In thesecases, preferably, the reducing agent may be directly mixed with thecontaminated matter. Alternatively, the reducing agent may be dissolvedinto water immediately before mixing with the contaminated matter.

[0085] When the reducing agent is in a form of powder, preferably, thepowder has a diameter up to 500 μm. Smaller diameters increase thedecomposition rate of the halogenated organic compound.

[0086] In some applications, the reducing is preferably a powder havinga diameter ranging from 0.001 millimeter to 5 millimeters and furtherpreferably a powder having a diameter ranging from 0.01 millimeter to 1millimeter. The diameter of the powder may control a rate of chemicalreduction reaction: as the diameter of the powder increases, the rate ofthe reduction reaction per unit weight of the reducing agent maydecrease. When the reducing agent is a metallic substance and has adiameter more than 5 millimeter, surfaces of the metal particle may becoated by a relatively thick oxide coating, the central part of themetal, which remains reduced, might not be used up. On the other hand,when the diameter is less than 0.001 millimeter, the rate of oxidationreaction is extremely fast: during transportation or mixing the reducingagent may contact with water and result in oxidation prior to use. Whenthe reducing agent is a metallic substance, oxidation in a surface ofthe powder may not affect oxidation of the inner part, which is notoxidized yet.

[0087] The heterotrophic anaerobic microorganism include, for example,methane producing microorganism such as those in the generaMethanosarcina, Methanothrix, Methanobacterium, and Methanobrevibacter;sulfate reducing microorganism such as those in the generaDesulfovibrio, Desulfotomaculum, Desulfobacterium, Desulfobacter,Desulfococcus; acid producing microorganism such as those in the generaClostridium, Acetivibrio, Bacteroides, Ruminococcus, and facultativeanaerobic microorganism such as those in the genera Bacillus,Lactobacillus, Aeromonas, Streptococcus, Micrococcus.

[0088] Microorganism in Bacillus, Pseudomonas, Aeromonas, Streptococcus,Micrococcus have an activity for reducing oxidized form of nitrogen, andtherefore they are preferable.

[0089] Nutrition sources of the heterotrophic anaerobic microorganism isselected depending on characteristics of microorganisms in thecontaminated matter. For example, one of a medium for methane producingmicroorganism, a medium for sulfate reducing microorganism, and a mediumfor nitrate reducing microorganism may be selected. In the selection, apurification treatability test may be conducted for each medium toinvestigate a purification rate of the halogenated organic compound.

[0090] For the methane producing microorganism, nutritional sourcesgenerally known as the nutritional sources for the growth of methaneproducing microorganisms may be used, such as lactic acid, methanol,ethanol, acetic acid, citric acid, pyruvic acid and polypeptone. For thesulfate reducing microorganisms, nutritional sources generally known asthe nutritional sources for the growth of sulfate reducingmicroorganisms may be used, such as lactic acid, methanol, ethanol,acetic acid, citric acid, pyruvic acid, polypeptone and an organicmatter containing a sugar.

[0091] Moreover, the nutritional sources for the growth of theheterotrophic anaerobic microorganisms include organic waste, which maybe either liquid or solid, and which is an object of purification bymethane fermentation. For example, such wastes include a waste waterfrom beer brewing, a waste water from starch production, a waste waterfrom dairy farming, beer lees, a refuse of tofu or been curd, and asludge.

[0092] When an excess amount of a liquid medium for microorganisms isadded to the contaminated matter, the halogenated organic compound mayfurther penetrate into the ground to aggravate the contamination. On theother hand, when too small an amount is added, sufficient water contentfor the growth of microorganisms may not be achieved and the growth maybe retarded. In view of the foregoing, the liquid medium formicroorganisms may be added so that a water content in the soil becomes25 to 60 percent and preferably 35 to 60 percent. This ratio apply tosludge also. An amount of the medium for microorganisms to be added maybe determined by considering a water content of the soil, a ratio ofpores in the soil, distribution of particle diameters of the soil, andcoefficients of water permeability through the soil. Therefore, both theconcentrations and the amount of the medium for microorganisms may vary,depending on conditions of contaminated soil, and determined by theresults of the purification treatability test.

[0093] It is effective to add diatomaceous earth or other water holdingmaterials, leaf mold or the like to soil for maintaining a water contentof the soil.

[0094] When the contaminated matter is substance which has low waterpermeability such as clay soil, hardened siltstone, the dechlorinationtreatment using only the reducing agent may have low contact efficiency,and it may take a long time, and the reducing condition may becomeunstable by supply of oxides from an ambient. In this case, an additionof organic carbons, which serve as growth substance for microorganisms,in addition to the reducing agent stabilize the reducing atmosphere in aneutral condition, thereby decomposing halogenated organic compound.

[0095] In the present invention, after adding the reducing agent to thecontaminated matter, preferably, the contaminated matter is maintainedunder a reducing atmosphere. The reducing atmosphere includes, forexample, an oxygen gas in air is blocked by water and so on. Theheterotrophic anaerobic microorganism may involve in decomposition ofthe halogenated organic compound, and the presence of the oxygen gas andso on may impede growth of such microorganisms. The oxidation of thereducing agent facilitates to achieve the reducing atmosphere. Aftercompletely consuming the reducing agent, there may be cases that thereducing atmosphere can not be maintained any longer.

[0096] Such reducing atmosphere preferably refers to a standardelectrode potential ranging from +200 mV to −2400 mV, further preferablyranging from +200 mV to −1000 mV, and furthermore preferably rangingfrom +100 mV to −600 mV at 25° C. with respect to the standard hydrogenelectrode.

[0097] In the present invention, while the reductive dehalogenationreaction proceeds, preferably, a prescribed pH is maintained.Specifically, pH of 5.8 to 8.5 is preferable, and pH of 6 to 8 isfurther preferable, and pH of 6.2 to 7.6 is furthermore preferable. Whenthe prescribed pH and anaerobic environment are maintained, an activityfor dehalogenation reaction on the surfaces of the reducing agent can bemaintained to be high.

[0098] A pH adjusting agent may be added to the contaminated matter.When the contaminated matter is acidic soil, preferably, the pHadjusting agent includes an alkali metal compound and an alkaline earthmetal compound. The pH adjusting agent may be conventional inorganicsoil improvers and include, for example, limestone, quick lime, slakedlime, calcium sulfate or gypsum, magnesium oxide, bentonite, pearlite,zeolite, and so on.

[0099] Preferably, various compost and compostable organic materials areadded to the contaminated matter to promote the reaction in thetreatment. The addition encompass adding microorganisms, addingnutritional sources, and promote holding water in the system. These maybe conventional organic soil improvers.

[0100] It is believed that the composts or compostable organic materialsmay serve as nutritional sources for microorganisms, may ensure theanaerobic environment around microorganisms, and may serve to decomposeand remove sulfur containing noxious gases such as hydrogen sulfide andmethylmercaptan, which result from anaerobic fermentation of soil.

[0101] It has been known that various composts contain fungi, bacteriaand many other various microorganisms, which include microorganismsbeing capable of efficiently decomposing sulfur containing noxioussubstances. A number of microorganisms useful for deodorizing have beenisolated from a variety of composts, and the composts are utilized forremoving noxious odors in treating droppings from domestic animals. Inview of the foregoing, the use of composts or compostable organicmaterials is preferable.

[0102] In the aforementioned conditions, the addition of inorganicsubstances, which serves as pH adjusting agents and may be referred toas inorganic soil improvers, such as alkali metal compounds and alkalineearth compounds; organic substances or organic soil improvers; and amedium for microorganisms to soil initiates growth of anaerobicmicroorganisms being present in the soil and forms a neutral andanaerobic environment in the soil. Therefore, the reduced iron, which isresponsible for chemical dehalogenation reaction in accordance with thepresent invention, may be mixed to the soil at the same time that theinorganic substances, the organic substances and the medium formicroorganisms are added thereto. Rather, the simultaneous addition ispreferable for ensuing to maintain an anaerobic condition for a longperiod of time and for reducing cost, thereby facilitating the processcontrol.

[0103] When the reductive dehalogenation in accordance with the presentinvention is practiced in actual contaminated site in the field, it isunnecessary to build large equipment. Various soil improvers and thereducing agent are mixed with the contaminated soil to be purified, andthen a medium for growth of microorganisms is added to the mixture, andthe area to be purified is covered with a polyvinyl sheet or the like sothat: water does not evaporate therefrom; that rain does not penetrateinto the soil; and that the area is kept warm. If desired, preferably,the surface of the soil of the area to be purified may be covered withleaf mold or compost for preventing release of noxious gases from thesoil and the evaporation of water therefrom.

[0104] A reaction mechanism of the reductive dehalogenation reaction hasnot been completely clarified. However, the present inventors speculatethe reaction mechanism as follows. Firstly, inorganic substances,organic substances, and medium for microorganisms, which serve as anagent for activating microorganisms, are added to the soil for ensuringpH 4.5 to 9.0 in the contaminated matter and for forming an anaerobicenvironment by utilizing growth of the microorganisms in the soil. Theanaerobic environment in the contaminated matter such as soil maycorrespond to a standard electrode potential ranging from +200 mV to−2400 mV at 25° C. with respect to the standard hydrogen electrode. Inthis case, the anaerobic microorganisms in the soil rapidly grow and donot impede chemical dehalogenation reaction, and therefore biologicaldehalogenation reaction and chemical dehalogenation reaction proceedsubstantially at the same time.

[0105] The mechanism for biological anaerobic dehalogenation has notbeen clarified since it has not been sufficiently investigated from theview point of microbiology and enzymology. However, since it has beenreported that strict anaerobic microorganisms such as methane producingmicroorganisms and sulfate reducing microorganisms and anaerobicmicroorganisms in a variety of anaerobic sludge and sediments undergoesa slow, microbiological dechlorination reaction of removing chlorineatoms one by one in anaerobic conditions, and therefore, it is believedthat similar, mild reductive dehalogenation reaction proceed inaccordance with the present invention.

[0106] In the present invention, during an initial state of a period ofabout one month from the beginning of the purification, chemicaldehalogenation reactions may predominate. Subsequently, as aconcentration of the contaminating halogenated organic compoundsdecreases and as the reducing agent decreases its reducing activity, thechemical dehalogenation reactions diminishes, and alternatively,biological dehalogenation reactions slowly become predominant, therebyfurther proceeding dehalogenation reactions. When the biologicaldehalogenation reactions are beginning to occur, the concentration ofcontaminating halogenated organic compounds have significantlydecreased, and therefore, it does not impede biological dehalogenationreactions. Actually, the biological reactions are suitable for purifyinga contaminated matter having a small concentration of halogenatedorganic compound, and the biological reactions proceed more active inthe small concentration. Therefore, a method for purifying mattercontaminated with halogenated organic compound in accordance with thepresent invention allows purification of the contaminated matter toextremely low concentrations by interaction of chemical dehalogenationreactions and biological dehalogenation reactions.

[0107] According to the chemical and biological, anaerobicdechlorination of the present invention, a combination of inorganicsubstances and organic substances, which may serve as soil improvers,and some of which may be hardly soluble in water, prevents release ofthe halogenated organic compound from the contaminated soil and allowsto keep an appropriate water holding ability so that the halogenatedorganic compound does not penetrate into further depth in the ground,thereby purifying the contaminated soil by the halogenated organiccompound for a short period of time with small cost.

[0108] The dechlorination reaction of the present invention can proceeduntil organic compounds being completely free of chlorine atom areobtained as main products, and this is preferable in view of completelypurifying the matter contaminated with halogenated organic compounds.For example, in purifying matter contaminated with tetrachloroethyleneand trichloroethylene, organic compounds being completely free ofchlorine atom, which are main products, are ethylene and ethane, and anintermediate containing a chlorine atom is hardly produced. Therefore,the result is very preferable.

[0109] In the second aspect of the present invention, the reducing agentof the first aspect of the present invention is used. In the secondaspect of the present invention, a prescribed nutritional source may notbe added, and the biological reaction may not be involved. Still, thesecond aspect of the present invention allows to decompose thehalogenated organic compound.

[0110] In accordance with the second aspect of the present invention,preferably, the reducing agent has the standard electrode potentialranging from −445 mV to −2400 mV at 25° C. with respect to the standardhydrogen electrode, and the reducing agent is at least one speciesselected from the group consisting of the iron-silicon alloy, thetitanium alloy, the zinc alloy, the manganese alloy, the aluminum alloy,the magnesium alloy, and the calcium alloy. The aforementioned reducingagents have an improved reducing power. Therefore, when the contaminatedmatter such as a soil contains an iron compound, particularly, an ironcompound of the second valence or the third valence, there arepossibilities that these iron compounds are reduced to an iron, therebyinvolving the dehalogenation reactions.

[0111] In view of the foregoing, preferably, the contaminated mattercomprises 0.1 g to 100 g of an iron compound based on 1 kg of a dryweight of the contaminated matter, and, further preferably, thecontaminated matter comprises 1 g to 100 g of an iron compound based on1 kg of a dry weight of the contaminated matter, and the iron compoundcomprises iron hydroxide (Fe(OH)₃) or triiron tetraoxide (Fe₃O₄). Theiron compound may further contain an iron oxide, such as FeO, Fe₂O₃ andthe like as well as iron chloride. Preferably, the reducing agent hasthe standard electrode potential ranging from −450 mV to −2400 mV at 25°C. with respect to the standard hydrogen electrode. Alternatively, thereducing agent may be a water soluble compound.

[0112] The reducing agent which is used in the third and fourth aspectsof the present invention is explained hereinafter. In the third aspectand fourth aspect of the present invention, the reducing agent having astandard electrode potential ranging from 130 mV to −2400 mV at 25° C.with respect to the standard hydrogen electrode is used. The reducingagent used in the first aspect and the second aspect of the presentinvention is preferably used.

[0113] However, the reducing agent used in the third aspect and fourthaspect of the present invention is not limited to the reducing agentused in the first aspect and the second aspect of the present inventionand include, for example, iron, which is not limited to the reduced ironand the cast iron, manganese, nickel, magnesium and copper. A largeamount of metallic iron and metallic manganese are present in a form ofoxides in the natural soil, and therefore the addition thereof hardlyinfluence the ecosystem and may be safe. Moreover, metallic iron andmetallic manganese are commercially available, and its access isconvenient. An amount of the reducing agent in used is the same asaforementioned.

[0114] Preferably, the reducing agent used in the third aspect andfourth aspect of the present invention is a metal having a standardelectrode potential ranging from −400 mV to −2400 mV at 25° C. withrespect to the standard hydrogen electrode. Preferably, the reducingagent is at least one species selected from the group consisting ofreduced iron, cast iron, iron-silicon alloy, titanium alloy, zinc alloy,manganese alloy, aluminum alloy, magnesium alloy, calcium alloy and awater soluble compound.

[0115] Alternatively, the reducing agent is a water soluble compound.Preferably, the reducing agent is a powder having a diameter up to 500μm.

[0116] The third aspect of the present invention is mainly explainedhereinafter. However, disclosure being the same as the first aspect ofthe present invention is omitted.

[0117] The third aspect of the present invention includes a step ofadding a reducing agent and a nutritional source for a heterotrophicanaerobic microorganism to the contaminated matter, the reducing agenthaving a standard electrode potential ranging from 130 mV to −2400 mV at25° C. with respect to the standard hydrogen electrode, therebydecomposing the halogenated organic compound by reductivedehalogenation, as aforementioned.

[0118] In the third aspect of the present invention, the nutritionalsource contains an organic carbon and 20 to 50 percent by weight, andpreferably 20 to 30 percent by weight, based on the organic carbon, ofan oxidized form of nitrogen. Consequently, in decomposing thehalogenated organic compound, a group of microorganisms involved inreductive dehalogenation reaction changes, thereby preventing the soilfrom changing its color into black by iron sulfate and noxious gasessuch as mercaptan from generating. When the oxidized form of nitrogen isa nitrate salt, for example, an amount of the oxidized form of nitrogenrefers to a weight of the nitrogen atoms in the nitrate salt. Similarly,an amount of the organic carbon refers to a weight of the carbon atomsin the organic matter.

[0119] Depending on the compositions of the nutritional source added,the reductive dehalogenation reactions involve biological reductionreactions such as reducing sulfate and methane fermentation in the soil,and there are chances that noxious gases such as hydrogen sulfide andmercaptan are produced and that a combustible gas such as a methane gasmay be generated. Moreover, a reaction of metallic powder and water inreducing conditions may produce a combustible hydrogen gas. Furthermore,sulfate reducing may produce iron sulfide, which may change color ofsoil into black.

[0120] However, the presence of 20 to 50 percent by weight, based on theorganic carbon, of an oxidized form of nitrogen can prevent theaforementioned reactions. Tests using soils have confirmed that theorganic carbon, which serves as a growth substrate, is predominantlyutilized by microorganisms having an activity of reducing oxidized formof nitrogen, and reactions such as methane fermentation and sulfurreduction are impeded. Nitrogen gas mainly generates from the soil. Eventhough a hydrogen gas generates, the hydrogen gas is diluted by thenitrogen gas, thereby eliminating a risk of explosion. Moreover, thenutritional source being free of a salt containing sulfur or sulfatefurther ensures to prevent the generation of sulfur containing gasessuch as hydrogen sulfide and mercaptan and of iron sulfide.

[0121] When an excess amount of the oxidized form of nitrogen is addedto the contaminated matter, the oxidized form of nitrogen remains evenafter consuming the organic carbon, and therefore it is difficult tomaintain a sufficiently reducing atmosphere. For example, an oxidationreduction potential with respect to the saturated silver chlorideelectrode may decrease to about +100 mV, and the reductivedehalogenation reactions may hardly proceed. On the other hand, only avery small amount oxidized form of nitrogen is added compared to anamount of the organic carbon added, the oxidized form of nitrogen may beconsumed up in an early stage by generation of the nitrogen gas, andsubsequently, standard biological dehalogenation reactions such asmethane fermentation may occur. Therefore, it is important to adjust aratio of the organic carbon and the oxidized form of nitrogen.

[0122]Alcaligenes eutrophus and Paracoccus denitrificans aremicroorganisms having an activity of reducing oxidized form of nitrogen,and the microorganisms in an aqueous solution consumes 40 to 50 percentby weight of the oxidized form of nitrogen based on the organic carbon.However, the present inventors conducted reduction reactions inaccordance with the present invention in a variety of soils by usingindigenous microorganisms, and the results show that the addition of 20to 50 percent by weight and preferably 20 to 30 percent by weight, basedon the organic carbon, of an oxidized form of nitrogen does not generatemethane and sulfur containing noxious gases and consumes the oxidizedform of nitrogen salts and achieves the complete dehalogenation of thehalogenated organic compounds.

[0123] Conventionally, it has been reported that the addition of theoxidized form of nitrogen impedes the reductive dehalogenation reactions(Fujita et al., Proc. of 8^(th) International Conf. on AnaerobicDigestion, 1997, Vol. 2, pages 492 to 499). However, the presentinvention adjusts a ratio of the organic carbon and the oxidized form ofnitrogen, thereby growing microorganisms having an activity of reducingoxidized form of nitrogen and preventing the generation of the sulfurcontaining noxious gases and the combustible gas such as the hydrogengas, as well as maintaining the reduction conditions in the contaminatedmatter and allowing to perform efficient dehalogenation reactions.Therefore, the third aspect of the present invention relates to a novelpurification method, which surpasses conventional wisdom.

[0124] Preferably, the oxidized form of nitrogen is in a form of anitrate salt. Preferably, the nitrate salt contains alkali metalnitrate, alkaline earth metal nitrate, iron nitrate, titanium nitrate,zinc nitrate, manganese nitrate, aluminum nitrate or magnesium nitrate.Further preferably, the nitrate salt contains sodium nitrate, potassiumnitrate or calcium nitrate.

[0125] In the present invention, preferably, the organic carbon issupplied as a water soluble organic carbon source. The features are notnecessarily limited to the third aspect of the present invention, andmay be applied to the first and fourth aspects of the present inventionalso. Preferably, the water soluble organic carbon source is a sugar, anorganic acid or derivative thereof, lower alcohol, a morasses waste, aliquor waste or a mixture thereof. The organic carbon serves as a growthsubstrate for growing microorganisms. The organic carbon may come fromsugars such as glucose, cane sugar; an organic acid or a salt thereofsuch as acetic acid, citric acid, and lactic acid; and an organic wasteliquid or an organic waste such as a morasses waste; a liquor waste,beer lees, a refuse of tofu or been curd. An amount of the organiccarbon to be added is selected, depending on the oxidizing power of thecontaminated matter and a concentration of the contaminating halogenatedorganic compounds. When the contaminated matter is a standard soil,about 1 gram of the organic carbon per one kilogram of the soil may benecessary to maintain reducing conditions. When the contaminated matterhas a concentration of the halogenated compound, which is an object ofdehalogenation, more than 50 milligram per kilogram, an amount of theorganic carbon may be required to increase by 10 to 20 milligram per 1milligram of the halogenated organic compound. However, these values maymerely rough estimates, and there are cases in an actual contaminatedsite that the organic carbons and the reducing power of the reducingagent is consumed by not only the oxidizing power of the contaminatedmatter but also the supply of water from rain and an oxygen gas in air.Therefore, in practicing the present invention, a preliminary test onsite should be conducted, and concentrations of the reducing agentshould be determined, depending on conditions on the site.

[0126] The fourth aspect of the present invention provides a method ofpurifying a contaminated matter containing a halogenated compound and asolid matter. The fourth aspect of the present invention includes thestep of mixing a prescribed reducing agent and a prescribed nutritionalliquid with the contaminated matter, and the mixing step includes a stepof adjusting the contaminated matter at pH ranging from 4.5 to 9.0.

[0127] In the present invention, preferably, the reducing agent may bein a powder form and wherein the nutritional liquid is added to thecontaminated matter and mixed thereof, and then the reducing agent isadded to the resultant mixture and further mixed thereof. The featuresallow to prevent the oxidation of the reducing agent by the nutritionalliquid, and the reducing power of the reducing agent can be exerted inthe contaminated matter.

[0128] Alternatively, the reducing agent may be a water solublecompound, and the reducing agent may be dissolved in the nutritionalliquid. The features allow to practice the present invention much easierthan a solid reducing agent in the contaminated site. Moreover, thefeatures allow to store and transport a large amount of the nutritionalliquid much easily. The nutritional liquid containing the reducing agentis preferably stored in a closed vessel for preventing the oxidation ofthe reducing agent during storage.

[0129] Alternatively, in the mixing step, the nutritional liquid may bedivided to at least two portions, and each portion may be added to thecontaminated matter one by one. When a large amount of nutritionalliquid is mixed with soil, for example, it is difficult to apply sheerforce onto lumps of soil in the liquid, and the lumps of soil may movein the liquid without breaking the lumps of soil. On the other hand,when only a small amount of nutritional liquid is added, it is mucheasier to apply sheer force onto lumps of soil for breaking the lumps,thereby allowing uniform mixing. Subsequently, a larger amount of thenutritional liquid may be added thereto. In one embodiment, preferably,1 to 10 percent by volume, based on the contaminated matter, of thenutritional liquid may be added to the contaminated matter and mixedthereof as a first step; and then an amount larger than the amount ofthe first step of the nutritional liquid may be added to thecontaminated matter and mixed thereof as a second step. In anotherembodiment, preferably, 1 to 5 percent by volume, based on thecontaminated matter, of the nutritional liquid may be added to thecontaminated matter and mixed thereof as a first step; the nutritionalliquid may be added to the contaminated matter and mixed thereof as asecond step wherein a sum of the nutritional liquids added in the firststep and the second step amounts 5 to 10 percent by volume, based on thecontaminated matter, of the contaminated liquid; and the nutritionalliquid is added to the contaminated matter and mixed thereof as a thirdstep wherein an amount of the nutritional liquid added in the third stepis more than an amount of the nutritional liquid added in either thefirst step or the second step. In either embodiment, only a small amountof the nutritional liquid is added in the first step so that the sheerforce is applied to the mixture, thereby facilitating a uniform mixture.In either embodiment, in overall 15 to 25 percent by volume, based onthe contaminated matter, of the nutritional liquid may preferably beadded to the contaminated matter. With regard to “in overall,” when thenutritional liquid is added to the contaminated matter by a plurality oftimes, the sum of all the nutritional liquid are referred to.

[0130] Subsequently, the mixture is kept in a condition that air hardlypenetrates through a matrix. In the keeping step, the reductivedehalogenation reaction removes the halogenated organic compound. Forexample, the mixture may be kept at least two weeks, and preferably atleast one month.

[0131] The keeping step is preferably carried out in a state where themixture is isolated from the surroundings for preventing the halogenatedorganic compounds in the mixture from diffusing into or permeatingthrough the surroundings.

[0132] Preferably, the contaminated matter is covered by a material thatdoes not penetrate so as to maintain a condition that air hardlypenetrates through a matrix. For example, the soil may be covered by apolyvinyl sheet, thereby promoting growth of the anaerobicmicroorganisms. Alternatively, the contaminated matter may be immersedin an aqueous liquid so as maintain a condition that air hardlypenetrates through a matrix.

[0133] Preferably, in the keeping step, the mixture is kept at atemperature ranging from 17° C. to 60° C. for at least initial threedays. There period allows to particularly promote the growth ofmicroorganisms in the mixture, increasing concentrations thereof.Preferably, in the keeping step, the mixture may be kept at atemperature ranging from 17° C. to 60° C. for at least initial fivedays. Further preferably, in the keeping step the mixture is kept at atemperature ranging from 20° C. to 40° C. for at least initial three,preferably five days.

EXAMPLE

[0134] The present invention is explained by way of exampleshereinafter. However, the present invention is not limited by theseexamples.

[0135] Tests for purifying tetrachloroethylene in examples in accordancewith the present invention used a medium for methane producingmicroorganisms of Table 1 or a medium for sulfate reducingmicroorganisms of Table 2 as a medium for microorganisms. Thesepurification tests are performed at room temperatures ranging from 12 to23° C.

[0136] Prior to determining its pH, each soil sample was adjusted tohave a ratio of the soil sample/pure water of being 1/1 by weight, anddetermined by a pH meter, HM-5B model produced by Toa Denpa Kogyo KK.Prior to determining an oxidation reduction potential with respect tothe saturated silver chloride electrode, each soil sample was adjustedto have a ratio of soil sample/oxygen-free water of being 1/1 by weight.An oxidation reduction potential meter ODIC-3 model produced by ToaDenpa Kogyo KK was used, An ORP composite electrode, PS-8160 model wasdipped in the conditioned soil sample for 30 minutes, and thereafter theORP value of the sample was measured.

[0137] To analyze ethylene chlorides present in soil, the methoddeveloped by the Yokohama National University (see K. Miyamoto et al.;“A Determination Method of Volatile Organic Pollutants in Soil”, theJournal of Japan Society on Water Environment, Vol. 18, No. 6, pp.477-488, 1995). Specifically, each soil sample was dipped in ethanol toextract ethylene and so on therefrom, and then the ethylene and so onobtained were further extracted with decane, and the solution ofethylene in decane was loaded into a column of Hitachi's G-5000 modelfor gas chromatography, in which the ethylene was analyzed by an FIDdetector.

[0138] Ethylene chloride gas generated in the gas phase was analyzedalso. The gas phase comprising the generated ethylene chloride gas wasloaded into a column of gas chromatography, and the ethylene gases wereanalyzed by using an FID detector. The column was 20 percent TCPChromosorb WAW DMCS, and the gas chromatography was Hitachi's G-5000model. To determine ethylene and ethane gases generated in the gasphase, the gas phase comprising the gases was loaded into a column ofPorapack Q column of Hitachi's G-5000 model for gas chromatography, inwhich said gases were analyzed by using an FID detector. To determinehydrogen, carbon dioxide and methane gases generated in the gas phases,GL Sciences Gas Chromatography 320 model and TCD detector were used withactive carbon 30/60 or Molecular Sieve 13 X.

[0139] As reduced iron, Wako first class reduced iron, product code096-00785 from Wako Pure Chemical Industries Ltd., Japan was used.Unless stated other wise, the reduce iron was powder.

Example 1

[0140] In Example 1, a powder of the reduced iron was used as thereducing agent.

[0141] A contaminated soil collected from a surface layer ofcontaminated soil in a factory A was used. The contaminant in thecontaminated soil was mainly tetrachloroethylene, and 25 mg oftetrachloroethylene was present in 1 kg of dry contaminated soil. 30gram of the contaminated soil was added to each of fourteen vials of avolume of 125 ml. The 14 samples were tested under 14 differentexperimental conditions, and changes over a period were determinedconcerning pH of the contaminated soil, an oxidation reduction potentialwith respect to the saturated silver chloride electrode thereof, and adecrease in tetrachloroethylene. The water content of each test systemranges from 48 to 53 percent. During the preparation of the sample ineach vial and after collecting the sample in the vial, the gas phase ofthe vial was replaced with a nitrogen gas.

[0142] The contaminated soil samples originated from a loam bed, ofwhich the physical characteristics were such that the water content was47 percent, the coefficient of water permeability was from 10⁻⁴ to 10⁻⁵cm/sec, the pH was 6.6, and the oxidation reduction potential withrespect to the saturated silver chloride electrode was 380 mV.

[0143] Test Conditions:

[0144] A. Reaction systems using a medium for methane producingmicroorganisms of Table 1:

[0145] {circle over (1)} Control of contaminated soil only

[0146] {circle over (2)} Contaminated soil+medium for methane producingmicroorganism (9.0 ml)

[0147] {circle over (3)} Contaminated soil+medium for methane producingmicroorganism (9.0 ml)+reduced iron (1.0 g)

[0148] {circle over (4)} Contaminated soil+medium for methane producingmicroorganism (9.0 ml)+reduced iron (1.0 g)+mixed lime fertilizer Aconsisting essentially of limestone (1.0 g)+compost of bovine droppings(1.0 g)+leaf mold (0.5 g)

[0149] {circle over (5)} Contaminated soil+methane producing medium (9.0ml)+reduced iron (1.0 g)+mixed lime fertilizer B consisting essentiallyof limestone and Azumin (1.0 g)+compost of sewage sludge (1.0 g)+leafmold(0.5 g)

[0150] {circle over (6)} Contaminated soil+methane producing medium (9.0ml)+reduced iron (1.0 g)+mixed shell fossil fertilizer consistingessentially of shell fossil (1.0 g)+compost of sewage sludge (1.0g)+leaf mold (0.5 g)

[0151] {circle over (7)} Contaminated soil+methane producing medium (9.0ml)+reduced iron (1.0 g)+mixed lime fertilizer A (1.0 g)+leaf mold (1.0g)

[0152]  “Azumin” used herein is a fertilizer containing humic acid andmagnesia, which comprises humic acid (50 to 60%), magnesia (15%), totalnitrogen (3%) and silicic acid (3%). TABLE 1 Medium for MethaneProducing Microorganisms Component Amount Tap Water 800 ml MineralSolution 1* 50 ml/liter Mineral Solution 2* 50 ml/liter Trace MineralSolution* 10 ml/liter Trace Vitamin Solution* 10 ml/liter NaHCO₃ 5.0g/liter Yeast Extract 1.0 g/liter Polypeptone 20 g/liter Glucose 25g/liter Sodium Citrate 25 g/liter Methanol 50 ml/liter L-cysteine HCISolution 5.0 ml/liter Na₂S.9H₂O Solution 5.0 ml/liter pH 6.9-7.2

[0153] containing 6 gram of K₂HPO₄ in 1 liter of distilled water.

[0154] *The Mineral Solution 2 refers to a solution containing 6 gram ofKH₂PO₄, 6 gram of (NH₄)₂(SO₄), 12 gram of NaCl, 2.6 gram of MgSO₄·7H₂Oand 0.16 gram of CaCl₂·2H₂O in 1 liter of distilled water.

[0155] *The Trace Mineral Solution refers to a solution containing 1.5gram of nitrilotriacetic acid, 3.0 gram of MgSO₄·7H₂O, 0.5 gram ofMnSO₄·2H₂O, 1.0 gram of NaCl, 0.1 gram of FeSO₄·7H₂O, 0.1 gram of CoSO₄or CoCl₂, 0.1 gram of CaCl₂·2H₂O, 0.1 gram of ZnSO₄·7H₂O, 0.01 gram ofCuSO₄, 0.01 gram of AlK(SO₄)₂, 0.01 gram of H₃BO₃, and 0.01 gram ofNa₂MoO₄·2H₂O in 1 liter of distilled water. The nitrilotriacetic acidwas dissolved while the solution was maintained at pH of 6.5 by KOH, andthen the other minerals were added. Finally, pH of the solution wasadjusted to 7.0 by KOH.

[0156] *The Trace Vitamin Solution refers to a solution containing 2 mgof biotin, 2 mg of folic acid, 10 mg of pyridoxine·HCl, 5 Mg ofthiamine·HCl, 5 mg of riboflavin, 5 mg of nicotinic acid, 5 mg ofcalcium DL-pantothenate, 0.1 mg of vitamin B₁₂, 5 mg of p-aminobenzoicacid, and 5 mg of lipoic acid.

[0157] Each of the aforementioned test condition refers to a reactionsystem, and its meaning in the case of {circle over (4)} is exemplifiedas follows:

[0158] To a 125-ml vial were added 30 g of a contaminated soil sample,1.0 g of reduced iron and 1.0 g of mixed lime fertilizer A, and amixture was mixed. To the resulting mixture was added 9.0 ml of themedium for methane producing microorganisms as shown in Table 1, andthereafter added 1.0 g of compost of bovine droppings and 0.5 g of leafmold. After the mixture was mixed in the vial, the vial was hermeticallysealed with a butyl rubber stopper and an aluminum seal. A series of theaforementioned procedures for preparing the samples were carried outspeedily without an interval.

[0159] The thus-prepared seven sample were stored. As shown in FIG. 1,the tetrachloroethylene content of each sample was measured on day 3,and the pH value and the oxidation-reduction potential with respect tothe saturated hydrogen chloride electrode thereof were measured on day7. The time intervals for the measurement are shown as in FIG. 1.

[0160] B. Reaction systems using a medium for sulfate-reducingmicroorganisms of Table 2:

[0161] {circle over (1)} Control of contaminated soil only

[0162] {circle over (2)} Contaminated soil+medium for sulfate-reducingmicroorganisms (9.0 ml)

[0163] {circle over (3)} Contaminated soil+medium for sulfate-reducingmicroorganisms (9.0 ml)+reduced iron (1.0 g)

[0164] {circle over (4)} Contaminated soil+medium for sulfate-reducingmicroorganisms (9.0 ml)+reduced iron (1.0 g)+mixed lime fertilizer Aconsisting essentially of limestone (1.0 g)+compost of bovine droppings(1.0 g)+leaf mold (0.5 g)

[0165] {circle over (5)} Contaminated soil+medium for sulfate-reducingmicroorganisms (9.0 ml)+reduced iron (1.0 g)+mixed lime fertilizer Bconsisting essentially of limestone and Azumin (1.0 g)+compost of sewagesludge (1.0 g)+leaf mold (0.5 g)

[0166] {circle over (6)} Contaminated soil+medium for sulfate-reducingmicroorganisms (9.0 ml)+reduced iron (1.0 g)+mixed shell fossilfertilizer consisting essentially of shell fossil (1.0 g)+compost ofsewage sludge (1.0 g)+leaf mold (0.5 g)

[0167] {circle over (7)} Contaminated soil+medium for sulfate-reducingmicroorganisms (9.0 ml)+reduced iron (1.0 g)+mixed lime fertilizer Aconsisting essentially of limestone (1.0 g)+leaf mold (1.0 g) TABLE 2Medium for sulfate-Reducing Microorganisms Component Amount Tap Water1000 ml K₂HPO₄ 0.5 g/liter NH₄Cl 1.0 g/liter Na₂SO₄ 1.0 g/literCaCl.2H₂O 0.1 g/liter MgSO₄.7H₂O 2.0 g/liter Yeast Extract 1.0 g/literFeSO₄.7H₂O 0.2 g/liter Trace Vitamin Solution* 10 ml/liter SodiumLactate 25 ml/liter Sodium Acetate 25 ml/liter Sodium Thioglycolate 0.1g/liter Ascorbic Acid 0.1 g/liter pH 6.6-7.0

[0168] *The Trace Vitamin Solution is the same as that in Table 1.

[0169] The test results of Example 1 are shown in FIG. 1 and FIG. 2.With regard to reaction systems A-6 and A-7 as well as reaction systemsB-6 and B-7, tetrachloroethylene decreased in the same way as A-4 andA-5 as well as reaction systems B-4 and B-5, and therefore, the resultsof the reaction systems A-6, A-7, B-6 and B-7were omitted in FIGS. 1 and2.

[0170] The results show that the addition of reduced iron, inorganicfertilizer and the compost along with either the medium for methaneproducing microorganisms or the medium for sulfate reducingmicroorganisms to the contaminated soil maintains a neutral atmosphereof about pH 7 and an anaerobic environment, thereby efficientlydecomposing tetrachloroethylene. FIG. 1 and FIG. 2 show that theaddition of the medium for methane producing microorganisms or themedium for sulfate reducing microorganisms alone to the contaminatedsoil hardly decompose tetrachloroethylene. When slaked lime was usedinstead of the mixed lime fertilizer A, the similar result was obtained.

Example 2

[0171] In Example 2, a powder of the reduced iron was used as thereducing agent. In control, iron (II) chloride or iron (II) sulfate wasused.

[0172] To the tetrachloroethylene contaminated soil collected from thefactory A as in Example 1 was added tetrachloroethylene to adjust afinal concentration of tetrachloroethylene of about 75 milligram per 1kg of the dry soil. Similar to Example 1, 30 gram of the contaminatedsoil was added to each of vials of a volume of 125 ml. The samples weretested under 8 different experimental conditions, and changes over aperiod were determined concerning pH of the contaminated soil, anoxidation reduction potential with respect to the saturated silverchloride electrode thereof, and a decrease in tetrachloroethylene. Thewater content of each test system ranges from 48 to 53 percent. Inreaction systems A-4 and B-4, the contaminated soil, compost of sewagesludge and leaf mold were sterilized with steam in an autoclave for 60minutes, thereby sterilizing microorganisms originated therefrom. Thesetests show the influence of the microorganisms in decomposingtetrachloroethylene.

[0173] During the preparation of the sample, the gas phase of the vialwas replaced with a nitrogen gas.

[0174] Test Conditions:

[0175] A. Reaction systems using the medium for methane producingmicroorganisms (Table 1):

[0176] {circle over (1)} Contaminated soil+methane producing medium (9.0ml)+reduced iron (1.0 g)+mixed lime fertilizer B consisting essentiallyof limestone and Azumin (1.0 g)+compost of sewage sludge (1.0 g)+leafmold (0.5 g)

[0177] {circle over (2)} Contaminated soil+methane producing medium (9.0ml)+FeCl₂ (1.0 g)+mixed lime fertilizer B consisting essentially oflimestone and Azumin (1.0 g)+compost of sewage sludge (1.0 g)+leaf mold(0.5 g)

[0178] {circle over (3)} Contaminated soil+methane producing medium (9.0ml)+FeSO₄ (1.0 g)+mixed lime fertilizer B consisting essentially oflimestone and Azumin (1.0 g)+compost of sewage sludge (1.0 g)+leaf mold(0.5 g)

[0179] {circle over (4)} Sterilized contaminated soil+methane producingmedium (9.0 ml)+reduced iron (1.0 g)+mixed lime fertilizer B consistingessentially of limestone and Azumin (1.0 g)+sterilized compost of sewagesludge (1.0 g)+sterilized leaf mold (0.5 g)

[0180] B. Reaction systems using the medium for sulfate-reducingmicroorganisms (Table 2):

[0181] {circle over (1)} Contaminated soil+sulfate-reducing medium (9.0ml)+reduced iron (1.0 g)+mixed lime fertilizer B consisting essentiallyof limestone and Azumin (1.0 g)+compost of sewage sludge (1.0 g)+leafmold (0.5 g)

[0182] {circle over (2)} Contaminated soil+sulfate-reducing medium (9.0ml)+FeCl₂ (1.0 g)+mixed lime fertilizer B consisting essentially oflimestone and Azumin (1.0 g)+compost of sewage sludge (1.0 g) leaf mold(0.5 g)

[0183] {circle over (3)} Contaminated soil+sulfate-reducing medium (9.0ml)+FeSO₄ (1.0 g)+mixed lime fertilizer B consisting essentially oflimestone and Azumin (1.0 g)+compost of sewage sludge (1.0 g)+leaf mold(0.5 g)

[0184] {circle over (4)} Sterilized contaminated soil+sulfate-reducingmedium (9.0 ml)+reduced iron (1.0 g)+mixed lime fertilizer B consistingessentially of limestone and Azumin (1.0 g)+sterilized compost of sewagesludge (1.0 g)+sterilized leaf mold (0.5 g)

[0185] The results of Example 2 are shown in Table 3 and Table 4.

[0186] Tables 3 and 4 show that the reduced iron decomposestetrachloroethylene. Namely, the addition of the reduced iron, inorganicfertilizer, serving as a pH adjusting agent, and a compost to thecontaminated soil, and further addition of either the medium for methaneproducing microorganisms or the medium for sulfate reducingmicroorganisms to the mixture stably ensure the neutral atmosphere ofabout pH 7 in an anaerobic atmosphere, thereby decomposingtetrachloroethylene in the soil. In contrast, the addition of FeCl₂ orFeSO₄ instead of the reduced iron to the contaminated soil hardlydecompose tetrachloroethylene. Namely, a ferrous salt such as FeSO₄ anda ferric salt such as FeCl₃ do not decompose tetrachloroethylene.

[0187] Where the microorganisms in the reactions systems were sterilizedin reaction systems A-4 and B-4, only a small amount oftetrachloroethylene was decomposed. The result suggests that reductivedehalogenation reactions in accordance with the present inventionproceeds synergistically with biological reactions and chemicalreactions.

[0188] Table 4 shows the result of the analysis of the gas componentsformed in the vials in reactions systems A-1 and B-1. In both reactionsystems, large amounts of hydrogen, carbon dioxide, ethylene and ethanegases were formed. In reaction systems A-1 and B-1, only an extremelytrance amounts of tetrachloroethylene and cis-DCE were detected. Vinylchloride is hardly detected, and the accumulation thereof was notobserved. In calculating the balance of the reactions in the reactionsystems A-1 and B-1, among a decomposed amount of thetetrachloroethylene in the soil, about 71 percent and about 58 percentof the tetrachloroethylene are converted into ethylene and ethane,respectively.

[0189] When an animal compost was used instead of the sewage sludgecompost, similar results were obtained. TABLE 3 Results of AnaerobicDehalogenation of Highly- Contaminated Soil (incubated for 55 days)Tested {circle over (1)} Reduced Matters Blank iron {circle over (2)}FeCl₂ {circle over (3)} FeSO₄ {circle over (4)} Sterilized [A] Mediumfor Methane producing Microorganisms pH 5.31 7.19 4.98 6.91 7.30 ORP*266 −288 90 −189 −47 PCE** 75 0.5 67 58 46 [B] Medium forSulfate-Reducing Microorganisms pH 5.31 7.55 4.89 7.39 7.36 ORP* 266−414 109 −138 −52 PCE** 75 6 61 51 55

[0190] TABLE 4 Gases Resulting from Anaerobic Dehalogenation ofTetrachloroethylene (incubated for 55 days) H₂ CO₂ CH₄ Ethylene EthaneUnit ml/kg-dry soil μmol/kg-dry soil Blank 0 30 0 0 0 Test A-{circleover (1)} 1270 1890 Trace 172 146 Test B-{circle over (2)} 770 1850 0138 101

[0191] Tetrachloroethylene was not decomposed into dichloroethylene orvinyl chloride but into ethylene and ethane.

Example 3

[0192] In Example 3, the reduced iron was used as the reducing agent.

[0193] Sludge samples, X and Y, were collected from a bottom of a lakeand from a surface of swamp, respectively. The lake and the swamp areadjacent to an industrial area. Tetrachloroethylene was added to thesludge samples to adjust a final concentration of 35 milligram oftetrachloroethylene in 1 kg of dry sludge. 15 kg of each of thecontaminated sludge samples was added to a cylinder made of stainlesssteel and having a volume of 25 liter. The cylinder has a diameter of300 mm and a height of 370 mm. Four experimental groups including acontrol group of the sample X, a purification group of the sample X, acontrol group of the sample Y, and a purification group of the sample Ywere prepared. The experimental conditions of the experimental groupsare as follows. The containers were covered by covers for preventingwater evaporation therefrom and entering any external water thereintoand for insulating the content of the cylinder. It is not essential toapply a compost and/or leaf mold onto a surface of each sludge sample,and therefore, the compost and the leaf mold were omitted. These fourgroups were set in open air, and time-dependent variations in pH values,the oxidation reduction potential with respect to saturated silverchloride electrode, a decrease in tetrachloroethylene were determined.During the test, temperatures in open air varied within the range of 7to 18° C. The water content of each sludge sample ranges from about 41to 50 percent.

[0194] Reaction systems

[0195] Control group of the X system: contaminated sludge and 3000 ml ofpure water

[0196] Purification group of X system: contaminated sludge, 3200 ml of awaste water from saccharified beer lees, 500 gram of reduced iron, 500gram of mixed lime fertilizer B containing limestones and Azumin as mainingredients, 500 gram of compost from sewage sludge, and 250 gram ofleaf mold

[0197] Control group of the Y system: contaminated sludge and 3300 ml ofpure water

[0198] Purification group of Y system: contaminated sludge, 3500 ml ofthe waste water from saccharified beer lees, 500 gram of reduced iron,500 gram of mixed lime fertilizer B containing limestones and Azumin asmain ingredients, 500 gram of compost from sewage sludge, and 250 gramof leaf mold

[0199] The waste water from saccharified beer lees contains 9600milligram per liter of reducing sugar, 180 milligram per liter of aceticacid, 3100 milligram per liter of lactic acid, and 8100 milligram perliter of a solid suspension. The waste water has biochemical oxygendemand of 12700 milligram per liter, and a concentration of the totalorganic carbon content of 5100 milligram per liter.

[0200] The result of the change in a concentration oftetrachloroethylene is shown in Table 5. With regard to pH and theoxidation reduction potentials (ORP) with respect to the saturatedsilver chloride electrode, both of the control groups of the system Xand the system Y had pH of from 4.6 to 5.3 and ORP of from 180 to 300mV, while the purification groups of the system X and the system Y hadpH of from 7 to 7.4 and ORP of from 400 to −570 mV. The results showthat a purification method in accordance with the present inventionallows that both the purification groups X and Y decomposetetrachloroethylene. TABLE 5 Changes of Concentrations ofTetrachloroethylene in Sediment (unit: mg/1 kg of dry sediment) Day 0Day 19 Day 28 Day 40 Day 57 Control of X system 33 30 28 29 30 PurifiedArea of X 28 9.3 5.9 2.7 1.8 system Control of Y system 35 28 30 27 29Purified Area of Y 31 16 10.6 6.1 3.3 system

[0201] According to the present invention, the combination of biologicalreactions and anaerobic biological reactions allows to rapidly andconveniently purify matter such as soil, groundwater and so oncontaminated with halogenated compounds. The method of the presentinvention purifies the contaminated matter without releasing halogenatedcompounds therefrom. For example, where soil is contaminated, the waterholding ability can be suitably adjusted so that halogenated organiccompounds do not penetrate into further depth in the ground.

[0202] The present invention allows to decompose the halogenated organiccompounds into organic compounds free of a halogen atom such as ethyleneand ethane. Therefore, the present invention is free from the problem ofaccumulating harmful intermediates.

Example 4

[0203] In Example 4, reduced iron or cast iron was used as the reducingagent.

[0204] In the tests for purifying tetrachloroethylene in soil in Example4, a medium for methane producing microorganisms of Table 6 was used.The oxidation reduction potential of Example 4 was determined when aplatinum electrode was used as the metallic electrode and the saturatedsilver chloride electrode was used as the comparing electrode. TABLE 6Medium for Methane Producing Microorganisms Component Amount Tap water880 ml Mineral Solution 1* 50 ml/l Mineral Solution 2* 50 ml/l TraceMineral Solution* 10 ml/l Trace Vitamin Solution* 10 ml/l NaHCO₃ 5.0 g/lYeast Extract 1.0 g/l polypepetone 2.0 g/l glucose 2.5 g/l sodiumcitrate 2.5 g/l methanol 50 ml/l L-cysteine chloride 0.1 g/l Na₂S.9H₂O0.1 g/l pH 6.9-7.2

[0205] The Mineral Solution 1, the Mineral Solution 2, the Trace MineralSolution, and the Trace Vitamin Solution are the same as those used inTable 1.

[0206] A contaminated soil collected from a surface layer ofcontaminated soil in a factory A was used. In the contaminated soil, 25mg of tetrachloroethylene was present in 1 kg of dry contaminated soil.30 gram of the contaminated soil was added to each of vials having avolume of 125 ml, and the medium for methane producing microorganisms,either reduced iron or scrap cast iron, a compost from sewage sludgewere added to the vial in conditions mentioned below, and thedecomposition of tetrachloroethylene was determined. Amounts of thereduced iron, the scrap cast iron, and the compost from sewage sludgeadded to the contaminated soil were 5 percent by weight. The scrap castiron was screened to separate scrap cast iron A having a diameter up to500 micrometers, scrap cast iron B having a diameter from 500 to 800micrometer, and scrap cast iron C having a diameter not less than 800micrometer. During the preparation of the sample in each vial, the gasphase of the vial was replaced with a nitrogen gas.

[0207] The water content of the soil in each test system ranges from48.4 to 48.9 percent. The water content herein is a value equal to(weight of water therein) divided by (a total weight of the wetcontaminated matter) multiplied by 100.

[0208] In the experiments, the samples were incubated for 60 days.Changes over a period were determined concerning pH of the contaminatedsoil, an oxidation reduction potential with respect to the saturatedsilver chloride electrode thereof, a decrease in tetrachloroethylene andamounts of ethylene, ethane, hydrogen, carbon dioxide, and methaneformed in the gas phase.

[0209] The reduced iron used in Example 4 is commercially available fromWako Pure Chemical Industries Ltd., as aforementioned.

[0210] Test Conditions

[0211] 4-1: Control of contaminated soil (30 g) (comparative example)

[0212] 4-2: Contaminated soil (30 g), a medium for methane producingmicroorganism (9.0 ml), reduced iron (1.5g), and a compost of sewagesludge (1.5 g)

[0213] 4-3: Contaminated soil (30 g), a medium for methane producingmicroorganism (9.0 ml), scrap cast iron A (1.5g), and a compost ofsewage sludge (1.5 g)

[0214] 4-4: Contaminated soil (30 g), a medium for methane producingmicroorganism (9.0 ml), scrap cast iron B (1.5g), and a compost ofsewage sludge (1.5 g)

[0215] 4-5: Contaminated soil (30 g), a medium for methane producingmicroorganism (9.0 ml), scrap cast iron C (1.5g), and a compost ofsewage sludge (1.5 g)

[0216] The results of Example 4 are shown in Tables 7 and 8.

[0217] Table 7 shows a concentration of tetrachloroethylene in soil whenpurified by scrap cast iron and so on.

[0218] Table 8 shows amounts of gases generated when purified by scrapcast iron and so on. TABLE 7 Results of Purifying Tetrachloroethylene inSoil by Scrap Cast Iron and so on (after 60 days of incubation) PCE^(a)ORP (mg/kg)^(b) pH (mV) 4-1 Contaminated soil(control) 23 6.63  307 4-2reduced iron + compost  0 7.58 −537 4-3 scrap cast iron A + compost  07.27 −375 4-4 scrap cast iron B + compost 16 7.25 −229 4-5 scrap castiron C + compost 20 7.27 −225

[0219] TABLE 8 Amounts of Gases in purifying Tetrachloroethylene in Soilby Scrap Cast Iron and so on. (after 60 days of incubation) conversionH₂ CH₄ CO₂ rate^(c) (ml/kg)^(b) (ml/kg)^(b) (ml/kg)^(b) 4-1 Contaminated0 0 0 Trace soil (control) 4-2 reduced iron + 79 3.4 trace 190 compost4-3 scrap cast iron 73 2.3 0 243 A + compost 4-4 scrap cast iron 25 1.60 366 B + compost 4-5 scrap cast iron 7.6 1.8 0 414 C + compost

[0220]^(b)mg per 1 kilogram of dry soil

[0221]^(c)conversion rate of ethylene and ethane fromtetrachloroethylene

[0222] In Table 7, values in the column PCE, pH, and ORP are those after60 days of incubation. In Table 8, the conversion rate of ethylene andethane from tetrachloroethylene refers to a ration of thetetrachloroethylene which is converted into ethylene and ethane. Valuesin the column H₂, CH₄ and CO₂ show amounts of gases generated in aperiod of the incubation per 1 kilogram of the dry soil.

[0223] In the reaction systems where the reduced iron and the scrap castiron A were used, tetrachloroethylene in the soil was purified to anundetected level.

[0224] The results show that, being similar to the reduced iron, thescrap cast iron dechlorinates tetrachloroethylene and converts intoethylene and ethane. Particularly, the use of the scrap cast iron A,which has small diameters very efficiently decomposetetrachloroethylene.

[0225] When the soil contaminated with tetrachloroethylene was purifiedby the scrap cast iron, pH of the soil remains about neutral and rangesfrom 7.2 to 7.3, and the oxidation reduction potential with respect tothe saturated silver chloride electrode ranges from −225 to −375 mVwhich indicates maintaining a reducing environment. Therefore, thecomparison of a purification process of soil using the reduced iron anda purification process of soil using the cast iron do not showsubstantial difference with respect to soil environment.

[0226] In all of the reaction systems which contains the medium formethane producing microorganisms, that is 4-2 to 4-5, a carbon dioxidegas was generated in the gas phase of the vials, suggesting thatmicroorganisms grew therein. We may conclude that the scrap cast iron donot impede growth of microorganisms in soil.

Example 5

[0227] To the soil of Example 4, which was contaminated withtetrachloroethylene, was further added tetrachloroethylene to obtainsoil samples having differing contents of tetrachloroethylene. Threesamples having 50 milligram of tetrachloroethylene, 75 milligram oftetrachloroethylene, and 140 milligram of tetrachloroethylene per 1 kgof dry soil were obtained. Purification tests were conducted to each ofthe contaminated soil samples.

[0228] Similar to Example 4, 30 gram of each of the contaminated soilsamples was added to each of vials having a volume of 125 ml, and 9.0 mlof the medium for methane producing microorganisms of Table 6, scrapcast iron A, which has a diameter up to 500 micrometers, and 1.5 gram ofa compost from sewage sludge were added to the vial, and thedecomposition of tetrachloroethylene was determined. During thepreparation of the sample in each vial, the gas phase of the vial wasreplaced with a nitrogen gas.

[0229] The water content of the soil in each test system ranges from48.4 to 48.9 percent. The water content herein is a value equal to[weight of water therein] divided by [a total weight of the wetcontaminated matter] multiplied by 100.

[0230] In the experiments, the samples were incubated for 63 days atroom temperature. Changes over a period were determined concerning pH ofthe contaminated soil, an oxidation reduction potential with respect tothe saturated silver chloride electrode thereof, a decrease intetrachloroethylene and amounts of ethylene and ethane formed in the gasphase.

[0231] Test Conditions

[0232] 5-1: Control of contaminated soil having 50 milligram oftetrachloroethylene per 1 kilogram of dry soil (30 g)

[0233] 5-2: Contaminated soil having 50 milligram of tetrachloroethyleneper 1 kilogram of dry soil (30 g), a medium for methane producingmicroorganism (9.0 ml), scrap cast iron A (1.5g), and a compost ofsewage sludge (1.5 g)

[0234] 5-3: Control of contaminated soil having 75 milligram oftetrachloroethylene per 1 kilogram of dry soil (30 g)

[0235] 5-4: Contaminated soil having 75 milligram of tetrachloroethyleneper 1 kilogram of dry soil (30 g), a medium for methane producingmicroorganism (9.0 ml), scrap cast iron A (1.5g), and a compost ofsewage sludge (1.5 g)

[0236] 5-5: Control of contaminated soil having 140 milligram oftetrachloroethylene per 1 kilogram of dry soil (30 g)

[0237] 5-6: Contaminated soil having 140 milligram oftetrachloroethylene per 1 kilogram of dry soil (30 g), a medium formethane producing microorganism (9.0 ml), scrap cast iron A (1.5g), anda compost of sewage sludge (1.5 g)

[0238] The results of Example 5 are shown in Table 9. TABLE 9 Results ofPurifying Soil Highly Contaminated by Tetrachloroethylene by Scrap CastIron (after 63 days of incubation) PCE^(a) conversion ORP (mg/kg)^(b)rate^(c) (%) pH (mV) 5-1 Contaminated 45 0 6.71 360 soil (control) 5-2scrap cast 4.0 65 7.28 −380 iron A +compost 5-3 Contaminated 73 0 6.75345 soil (control) 5-4 scrap cast 19 58 7.19 −375 iron A +compost 5-5Contaminated 139 0 6.86 336 soil (control) 5-6 scrap cast 78 28 7.31−347 iron A +compost

[0239] In the present invention, the use of a cast iron powder or areduced iron powder allows to purify contaminated matter with a widerange of concentrations of halogenated organic compounds with a highpurification rate. Use of cast iron, for example, scrap cast iron purifysafely and conveniently matter contaminated with halogenated organiccompounds with low cost. Moreover, the industrial waste may be recycled.

[0240] Furthermore, use of a soil improver having a low solubilityallows to prevent releasing halogenated organic compounds from thecontaminated matter. Moreover, the water holding ability of the soil canbe suitably adjusted so that halogenated organic compounds do notpenetrate into further depth in the ground.

Example 6

[0241] Example 6 corresponds to the second aspect of the presentinvention. Example 6 shows that it is capable of decomposing halogenatedorganic compounds without adding a nutritional source of heterotrophicanaerobic microorganisms.

[0242] In Example 6, as the reducing agents, (1) metallic iron(comparative example), (2), manganese, (3) an aluminum-silicon alloy,and (4) sodium hypophosphite (NaPH₂O₂) are used, and the results arecompared.

[0243] Standard electrode potentials of the reducing agents are shown inTable 10. TABLE 10 Standard Electrode Potential of Reducing AgentsStandard Electrode Reducing Agent Potential (mV) (1) Metallic Iron −440(2) Manganese −1180 (3) Aluminum-Silicon Alloy −1600 (4) Sodiumhypophosphite −499

[0244] To each of 6500 gram of soil originated from a loam bed,containing 150 milligram per kilogram of tetrachloroethylene and has awater content of 60 percent was added (1) 20 gram of metallic iron, (2)10 gram of manganese, (3) 10 gram of aluminum-silicon alloy and (4) 20gram of sodium hypophosphite (NaPH₂O₂), respectively, followed bymaintaining temperature of 20° C. Following conditions were monitored.

[0245] In runs (2) and (3), oxidation reduction potentials reduced tonot more than −500 mV within one hour, and maintained at not more than−500 mV in a period of 10 days therefrom. Tetrachloroethylene thereinwas completely dehalogenated into ethylene and ethane. In run (4),oxidation reduction potential reduced to not more than −450 mV withinone hour, and maintained at not more than −450 mV in a period of 10 daystherefrom. Tetrachloroethylene therein was completely dehalogenated intoethylene and ethane. In contrast, in run (1), it took five days toreduce oxidation reduction potential to −400 mV, and oxidation reductionpotential was maintained at not more than −400 mV for a period ofanother five days therefrom. 20 percent of tetrachloroethylene wasdehalogenated into ethylene and ethane within a total period of 10 daysfrom the addition.

Example 7

[0246] (1) A system where a reducing agent was solely added, and wherean organic carbon source was not added was compared with (2) a systemwhere both the reducing agent and the organic carbon source were added.As the reducing agent, a calcium silicon alloy having a standardelectrode potential of −1900 mV was used, and as the organic carbonsource, sodium acetate was used.

[0247] To 65 kg of a clay soil having 200 milligram per kilogram oftrichloroethylene and having a water content of 55 percent was added 100gram of the calcium silicon alloy in the system (1) and (2). In thesystem (2), 70 gram of sodium acetate and 7 gram of nutritional saltswere further added. Both systems were maintained at temperature of 20°C., and following conditions were monitored.

[0248] In both systems (1) and (2), oxidation reduction potentialsreduced to not more than −500 mV within one hour. In system (1), theoxidation reduction potential was maintained at not more than −500 mV ina period of 10 days therefrom. Subsequently, the oxidation reductionpotential gradually increases toward the oxidation side to the extent of0 mV after a period of 40 days. 80 percent of trichloroethylene wasreduced to ethylene and ethane while 20 percent thereof remained in thesoil. On the other hand, in system (2), the oxidation reductionpotential maintained at not more than −500 mV in a period of 40 daystherefrom, and 99 percent of tetrachloroethylene therein was reducedinto ethylene and ethane.

[0249] A surface of the reducing agent of the present invention ishardly coated by a stable oxidation film, and the reducing agent iseasily dissolved to water, thereby facilitating a contact withcontaminated matter and increasing a rate of decomposition. Even whenthe contaminated matter is clay soil or hardened siltstone, both ofwhich have low water permeability, combination of the reducing agent andan organic carbon source, which serves as a growth substance formicroorganisms, allows dehalogenation reactions.

Example 8

[0250] In Example 8, as the reducing agents, (1) metallic iron(control), (2) a powder of sodium hypophosphite (NaPH₂O₂), and (3) anaqueous solution of titanium citrate are used, and the results arecompared.

[0251] Test Conditions

[0252] A loam soil having 120 milligram of tetrachloroethylene perkilogram upon conversion into dry soil was used. An initial oxidationreduction potential was +350 mV, and an amount of the soil was 100 m³.In systems (2) and (3), oxidation reduction potentials reduced to notmore than −450 mV within one hour, and the oxidation reductionpotentials were maintained at not more than −450 mV in a subsequentperiod of 5 days. Trichloroethylene was dehalogenated into ethylene andethane by the fifth day.

[0253] On the other hand, in system (1), one backhoe was used to mix thesoil with the metal, and it took ten days to mix thereof. Subsequently,it took another five days until an oxidation reduction potential reducedto −400 mV, and the oxidation reduction potential maintained at not morethan −400 mV in an additional period of 5 days therefrom. In the totalperiod of 20 days, 20 percent of tetrachloroethylene therein wasdehalogenated into ethylene and ethane.

Example 9

[0254] In either system, ascorbic acid was used as the reducing agent.In system (1), an organic carbon source was not added. In contrast, insystem (2) sodium acetate as the organic carbon source was used.

[0255] A clay having 100 milligram of tetrachloroethylene per kilogramupon conversion into dry soil was used. An initial oxidation reductionpotential was +320 mV, and an initial pH was 6.5.

[0256] Test Result

[0257] In both systems (1) and (2), oxidation reduction potentials werereduced to not more than +130 mV within one hour. In system (1), theoxidation reduction potential was maintained at not more than +130 mV ina period of 10 days therefrom. Subsequently, the oxidation reductionpotential gradually increased toward the oxidation side to the extent of+300 mV after a period of 40 days. A pH of 6.3 on the initial daygradually decreased to pH of 5.5 after a period of 40 days. 50 percentof trichloroethylene was reduced to ethylene and ethane while 50 percentthereof remained in the soil.

[0258] On the other hand, in system (2), the oxidation reductionpotential gradually decreased to the extent of not more than −150 mVafter a period of 20 days, and maintained at not more than −150 mV in aperiod of 40 days therefrom. A pH of 7.5 on the initial day graduallydecreased to pH of 6.8 after a period of 40 days. 99.9 percent oftetrachloroethylene therein was reduced into ethylene and ethane.

[0259] In these embodiments, the use of the water soluble reducingagents allows to effectively contact the reducing agent with mattercontaminated with a halogenated compound, thereby promoting reductivedehalogenation reactions.

[0260] Moreover, the reducing agent in use for these embodiments has astandard electrode potential substantially equal to or smaller thanmetallic iron so as to increase a potential difference from thehalogenated organic compound, thereby accelerating a rate ofdehalogenation. Even when the contaminated matter is clay soil orhardened siltstone, both of which have low water permeability,combination of the reducing agent and an organic carbon source, whichserves as a growth substance for microorganisms, allows dehalogenationreactions. Moreover, the reducing agent does not become passivated,contrary to metallic iron.

Example 10

[0261] Example 10 shows that a method of the present invention iscapable of decomposing a halogenated aromatic compound.

[0262] To 6 kilogram of a loam soil having a concentration of 10milligram per kilogram of pentachlorophenol, which is referred to asPCP, was added 20 gram of reduced iron. In system 10-1, one liter of amedium for nitrate reducing microorganisms of Table 11 was addedthereto. On the other hand, in system 10-2, as a control, one liter ofwater was added thereto. TABLE 11 Medium for Sulfate ReducingMicroorganisms component amount potassium nitrate 4.5 g/l potassiumacetate 8.5 g/l sodium hydrogen carbonate 5.0 g/l magnesium chloridehexahydrate 0.2 g/l yeast extract 0.1 g/l diluting water tap water pH6.9˜7.4

[0263] Subsequently, the mixture was mixed, and the resultant mixturewas maintained at 28° C. Changes of a PCP concentration and a productconcentration were monitored.

[0264] Results are shown in Tables 12 and 13. TABLE 12 Result of System10-1 Compound initial day after 20 days after 40 days PCP (mg/kg) 10.10.58 0.01 TeCP (mg/kg) 0.00 2.0 0.00 CP (mg/kg) 0.00 2.3 0.02 Phenol0.00 1.2 3.1 Eh (mV) +312 −380 −423

[0265] TABLE 13 Result of System 10-2 Compound initial day after 20 daysafter 40 days PCP (mg/kg) 10.2 2.4 0.9 TeCP (mg/kg) 0.00 1.0 0.00 CP(mg/kg) 0.00 2.1 2.8 Phenol 0.00 0.8 1.0 Eh (mV) +308 −170 +118

[0266] In Tables 12 and 13, TeCP and CP are 2,3,5,6-tetrachlorophenoland 3-chlorophenol, respectively. Eh is a converted value of a standardelectrode potential with respect to the standard hydrogen electrode.

[0267] In system 10-1, compared to system 10-2, pentachlorophenol wasrapidly decomposed. It is believed that, in system 10-1,pentachlorophenol was decomposed into phenol by means of2,3,5,6-tetrachlorophenol and/or 3-chlorophenol.2,3,5,6-tetrachlorophenol and 3-chlorophenol were dehalogenated and didnot accumulate. It is believed that phenol was decomposed into othercompounds.

Example 11

[0268] Example 11 mainly corresponds to the third aspect of the presentinvention.

[0269] In Example 11, a medium for oxidized-nitrogen reducingmicroorganisms of Table 14 and a medium for methane producingmicroorganisms of Table 15 as a control were used to purify a soilcontaminated with tetrachloroethylene. In Table 14, the oxidized form ofnitrogen corresponds to 23 percent by weight of the organic carbon. Thepurification test was carried out at room temperature ranging from 12 to23° C. for 30 days. Changes in properties of the soil were monitored,and results were shown in Table 16.

[0270] Prior to determining its pH, each soil sample was adjusted tohave a ratio of the soil sample/pure water of being 1/1 by weight, anddetermined by a pH meter, HM-5B model produced by Toa Denpa Kogyo KK.Prior to determining an oxidation reduction potential with respect tothe saturated silver chloride electrode, each soil sample was adjustedto have a ratio of soil sample/oxygen-free water of being 1/1 by weight.An electrode was dipped into a sample liquid for 30 minutes using anoxidation reduction potential meter UK-2030 from Central Science, andthereafter the ORP value of the sample was measured. An oxidationreduction potential with respect to the saturated silver chlorideelectrode in the present Example refers to a potential determined by aplatinum electrode serving as a metal electrode and the saturated silverchloride serving as a comparing electrode.

[0271] To analyze ethylene chlorides present in soil, the methoddeveloped by the Yokohama National University (see K. Miyamoto et al.;“A Determination Method of Volatile Organic Pollutants in Soil”, theJournal of Japan Society on Water Environment, Vol. 18, No. 6, pp.477-488, 1995). Specifically, each soil sample was dipped in ethanol toextract ethylene and so on therefrom, and then the ethylene and so onobtained were further extracted with decane, and the solution ofethylene in decane was loaded into a column of Hitachi's G−5000 modelfor gas chromatography, in which the ethylene was analyzed by an FIDdetector. To determine ethylene and ethane gases generated in the gasphase, the gas phase comprising the gases was loaded into a column ofPorapack Q column of Hitachi's G−5000 model for gas chromatography, inwhich said gases were analyzed by using an FID detector. To determinehydrogen, carbon dioxide and methane gases generated in the vapor gases,GL Sciences Gas Chromatography 320 model and TCD detector were used withactive carbon 30/60 or Molecular Sieve 13 X. Ion concentrations of anitrate form of nitrogen and a nitrite form of nitrogen were determinedby introducing an extract water being adjusted to have a ratio of thesoil sample/pure water of being 1/1 by weight into Hitachi anionchromatography 2010i. TABLE 14 Medium for Oxidized-Nitrogen ReducingMicroorganisms component amount potassium nitrate 4.5 g/l potassiumacetate 8.5 g/l sodium hydrogen carbonate 5.0 g/l magnesium chloridehexahydrate 0.2 g/l yeast extract 0.1 g/l diluting water tap water pH6.9˜7.4

[0272] TABLE 15 Medium for Methane Producing Microorganisms ComponentAmount L-cysteine HCI Solution 0.1 g/l Polypeptone 2.0 g/l Glucose 2.5g/l Sodium Citrate 2.5 g/l Methanol 5.0 ml/l Sodium Hydrogen Carbonate5.0 g/l Sodium Sulfide Nonahydrate 0.1 g/l yeast extract 1.0 g/lDiluting Water tap water pH 6.9˜7.2

[0273] A purification test was conducted on a soil contaminated bytetrachloroethylene with a concentration of about 25 milligram per 1kilogram of dry soil and collected from a surface layer of contaminatedsoil in a chemical factory. 30 gram of the contaminated soil was addedto a vial of a volume of 50 ml, and then the medium and the metallicpowder as mentioned below was mixed therewith. After a period of 30days, changes of soil properties such as decomposition oftetrachloroethylene were determined as shown in Table 16.

[0274] As the metallic powder, Wako first class reduced iron from WakoPure Chemical Industries Ltd., Japan was used. During the preparation ofthe sample, the gas phase of the vial was replaced with a helium gas.

[0275] Experimental Conditions

[0276] 10-1 30 gram of contaminated soil

[0277] 10-2 30 gram of contaminated soil, 9.0 ml of water and 0.07 gramof the reduced iron

[0278] 10-3 30 gram of contaminated soil, 9.0 ml of the medium foroxidized-nitrogen reducing microorganisms, and 0.07 gram of the reducediron

[0279] 10-4 30 gram of contaminated soil, 9.0 ml of the medium formethane producing microorganisms, and 0.07 gram of the reduced iron

[0280] The result is shown in Table 16. When the medium foroxidized-nitrogen reducing microorganisms was used, it was confirmedthat tetrachloroethylene was dechlorinated into ethylene and ethane andthat color change of the soil into black and generations of methane gas,mercaptan odor were prevented. It was found that generation of anitrogen gas diluted a hydrogen gas. We found that nitrate and nitritedid not remain in the soil.

[0281] On the other hand, in the system that only the metal and waterwere added, pH drastically decreased, and the oxidation reductionpotential with respect to the saturated silver chloride increased to +2mV. As a result, a sufficient reductive dechlorination decomposition wasnot observed. A portion of tetrachloroethylene remained in the soil, andonly 26 percent was converted into ethylene. Therefore, the result showsthat it is difficult to maintain an appropriate reduction state over along period of time in the system where only the metal powder was addedand that the further addition of a nutritional agent and resultantbiological reactions allow stable decomposition. In the system whereonly the metallic powder was added, a hydrogen gas of a concentration ofabout 100 percent was generated, and there was a risk of explosion. Onthe other hand, in the system where the medium for oxidized-nitrogenreducing microorganisms, a nitrogen gas was generated and diluted thehydrogen gas. Similarly, in the system where the medium for methaneproducing microorganisms was added, a methane gas was generated anddiluted the hydrogen gas. Therefore, these systems are safer. However,in the system where the medium for methane producing microorganisms wasadded, an odor was generated, and color of the soil changed into black.TABLE 16 Results of Purifying Tetrachloroethylene (PCE) in Soil (after30 days of incubation) 10-1 10-2 10-3 10-4 PCE in soil 22.5 8.6 0.0 0.0(mg-PCE/kg) pH 6.82 5.37 7.48 7.52 ORP(mV) +289 +2 −376 −542 Conversionrate of 0 26 81 84 PCE to ethylene and ethane (%) H₂(ml/kg-soil) 0.001.3 2.8 3.5 CH₄(ml/kg-soil) 0.00 0.07 0.00 0.52 CO₂(ml/kg-soil) 0.000.15 0.10 182 N₂(ml/kg-soil) 0.05 0.04 110 0.01 NO₃-N(ml/kg-soil) 0.50.3 0.0 0.0 NO₂-N(ml/kg-soil) 0.0 0.0 0.0 0.0 Odor none none nonepresent Coloration none a portion changed changed changed into pale intointo pale black dark black brown

[0282] In the third aspect of the present invention, use of thenutritional source containing an organic carbon and 20 to 50 percent byweight, based on the organic carbon, of an oxidized form of nitrogenprevents soil from changing to black and noxious gases such as mercaptanfrom being generated during decomposition of halogenated organiccompounds.

Example 12

[0283] In Example 12, an organic carbon was supplied as a water solubleorganic carbon source.

[0284] To 5 kilogram of each soil having a water content of 60 percentand having organic chlorinated compounds with a concentration of 10milligram per kilogram was added 6 gram of (1) glucose, (2) morasses and(3) a compost, respectively. In addition, 200 milligram of nutritionalsalts were added to each soil sample, and a mixture was maintained at28° C.

[0285] Subsequent conditions were monitored.

[0286] In systems (1) and (2), anaerobic microorganisms proliferated to10⁷ microorganisms per gram of the soil in a period of several days. Anoxidation reduction potential with respect to the saturated silverchloride electrode was maintained to not more than −600 mV in a periodof 30 days, and tetrachloroethylene was dehalogenated into ethylene andethane.

[0287] On the other hand, in system (3), it took 20 days to proliferatemicroorganisms to 10⁷ microorganisms per gram of the soil. The oxidationreduction potential increased after the 13^(th) day, and the oxidationreduction potential reaches to −23 mV at the 30^(th) day. 50 percent oftetrachloroethylene remained in the soil in a form ofcis-dichloroethylene so that a complete dehalogenation was not achieved.

Example 13

[0288] To 200 kilogram of each soil having a water content of 65 percentand having halogenated organic compounds with a concentration of 30milligram per kilogram was added 240 gram of glucose and 8 gram ofnutritional salts were added. As a purification operation in winter, insystem (1), the soil was surrounded by a polyvinyl house, and heated bywarm water to an average temperature of 22° C.; and in system (2), thesoil was stacked in open field.

[0289] In system (1), anaerobic microorganisms proliferated to 10⁷microorganisms per gram of the soil in a period of several days. Anoxidation reduction potential with respect to the saturated silverchloride electrode was maintained to not more than −600 mV in a periodof 30 days, and tetrachloroethylene was dehalogenated into ethylene andethane.

[0290] On the other hand, in system (3), it took 30 days to proliferatemicroorganisms to 10⁷ microorganisms per gram of the soil. The oxidationreduction potential increased after the 10^(th) day, and the oxidationreduction potential reaches to +52 mV at the ₃₀th day. 20 percent oftetrachloroethylene remained as it is in the soil, 40 percent oftetrachloroethylene remained in the soil in a form ofcis-dichloroethylene.

Example 14

[0291] Example 14 mainly corresponds to the fourth aspect of the presentinvention.

[0292] Engineering work of purifying matter contaminated withhalogenated organic compounds were carried out on the site.

[0293] Soil was extracted from the ground of a chemical plant, andtransferred to a concrete pit. The soil was contaminated withtetrachloroethylene with an average concentration of about 11 milligramper kilogram of soil.

[0294] Engineering work was carried out on the soil in the followingthree processes.

[0295] Process 1

[0296] Using a backhoe, 5 m³ of the contaminated soil in the concretepit was added to a bucket made of stainless steel having a volume of 10m³, which serves as a container that does not leak water. Subsequently,0.2 m³, which corresponds to 4 percent by volume of the soil, of anutritional liquid, which is referred to as nutritional agent A,containing the medium for oxidized-nitrogen reducing microorganisms ofTable 14 and the medium of methane producing microorganisms of Table 15,was added to the steel bucket, and then the soil was mixed with thenutritional agent A, using the backhoe. Then, 0.2 m³, which correspondsto 4 percent by volume of the soil, of the nutritional agent A wasfurther added to the bucket, and the soil was mixed with the nutritionalagent A, using the backhoe. Subsequently, 0.7 m³, which corresponds to14 percent by volume of the soil, of the nutritional agent A, was addedto the bucket, and the soil was mixed with the nutritional agent A.After the soil is sufficiently mixed with the nutritional agent A,reduced iron was distributed over the soil in the bucket, and furthermixed therewith. The mixed soil was transferred back into the concretepit.

[0297] Process 2

[0298] Using a backhoe, 5 m³ of the contaminated soil in the concretepit was added to the aforementioned bucket made of stainless steel.Subsequently, 1.1 m³, which corresponds to 22 percent by volume of thesoil, of the nutritional agent A was added to the bucket, and the soilwas mixed with the nutritional agent A, using the backhoe. After thesoil is sufficiently mixed with the nutritional agent A, reduced ironwas added to all over the contaminated soil in the steel bucket, andfurther mixed therewith. The mixed soil was transferred back into theconcrete pit.

[0299] Process 3

[0300] Using a backhoe, 5 m³ of the contaminated soil in the concretepit was added to the aforementioned bucket made of stainless steel.Within fifteen to twenty hours from the addition, 0.2 m³, whichcorresponds to 4 percent by volume of the soil, of a suspensionincluding the medium for oxidized-nitrogen reducing microorganisms ofTable 14, the medium of methane producing microorganisms of Table 15,and reduced iron suspended therein was added to the bucket. Thesuspension is referred to a nutritional agent B hereinafter. The soilwas mixed with the nutritional agent B, using the backhoe. Then 0.2 m³,which corresponds to 4 percent by volume of the soil, of the nutritionalagent B was added to the bucket, and the soil was mixed with thenutritional agent B, using the backhoe. Subsequently, 0.7 m³, whichcorresponds to 14 percent by volume of the soil, of the nutritionalagent B, was added to the bucket, and the soil was mixed with thenutritional agent B. After the soil is sufficiently mixed with thenutritional agent A, reduced iron was distributed over the soil in thebucket, and further mixed therewith. The mixed soil was transferred backinto the concrete pit.

[0301] Portions of the soil mixed in processes 1 to 3 were screenedthrough a screen with 10 mm meshes to determine an amount of lumps inthe mixed soils by naked eyes. In processes 1 and 3, the mixed soilscontained 1 to 10 percent of lumps in the soils. In contrast, the mixedsoil of process 2 contained 15 to 30 percent by lumps in the soil. Theresults show that a degree of mixture depends on a method of adding anutritional liquid and a method of mixing thereof.

[0302] In any of processes of 1 to 3, after the mixture, all of theupper surfaces of the soil in the concrete pit was covered by apolyvinyl sheet and the polyvinyl sheet was fixed by a steel plate sothat oxygen transfer with the external environment was prevented.Alternatively, instead of covering with the polyvinyl sheet, water maybe added to immerse the soil such that the water level is higher by 5 to15 centimeter than the upper surface of the soil so that oxygen transferwith the external environment is prevented and that a water content inthe soil is sufficiently maintained.

[0303] In any of processes 1 to 3, the soil was transferred back intothe concrete pit for preventing tetrachloroethylene eluting away. Inactual practice, the contaminated soil from the ground may be added to abucket, and the contaminated soil may be mixed with a nutritional liquidin the bucket, and then the mixture may be transferred back into a pit,which was formed by removing the contaminated soil. Alternatively,instead of mixing in the bucket, the soil may be mixed in the ground onthe spot.

[0304] After covering the soil by the polyvinyl sheet for two months, atetrachloroethylene concentration in the soil was determined. Theresults are shown in Table 17. TABLE 17 Results of Engineering Work ofPurifying Soil Contaminated with Tetrachloroethylene (PCE) ProcessProcess Process Period 1 2 3 PCE concentration (mg/1) 5 5 5 on theinitial day PCE concentration (mg/1) 0.01 0.55 1.9 after two monthsdecomposition rate (%) 99.8 89 62

[0305] In the soil mixed in the process 1, 2, and 3, 99.8 percent, 89percent, and 62 percent of tetrachloroethylene was decomposed,respectively. The result of process 1 shows that additions of thenutritional agent at a plurality of times and mixing for each timeincreases decomposition rate. The result of process 2 shows that anaddition of a reducing agent in a powder form subsequent to mixing thesoil with the nutritional liquid increase the decomposition rate.

1. A method for purifying matter contaminated with a halogenated organiccompound, which method comprises the step of: adding a reducing agentand a nutritional source for a heterotrophic anaerobic microorganism tothe contaminated matter, the reducing agent having a standard electrodepotential ranging from 130 mV to −2400 mV at 25° C. with respect to thestandard hydrogen electrode, the reducing agent being at least onespecies selected from the group consisting of reduced iron, cast iron,an iron-silicon alloy, a titanium alloy, a zinc alloy, a manganesealloy, an aluminum alloy, a magnesium alloy, a calcium alloy and a watersoluble compound.
 2. A method of claim 1 wherein the reducing agent hasa standard electrode potential ranging from −400 mV to −2400 mV at 25°C. with respect to the standard hydrogen electrode, and the reducingagent is at least one species selected from the group consisting of thereduced iron, the cast iron, the iron-silicon alloy, the titanium alloy,the zinc alloy, the manganese alloy, the aluminum alloy, the magnesiumalloy, and the calcium alloy.
 3. A method of claim 1 wherein thereducing agent comprises the reduced iron.
 4. A method of claim 1wherein the reducing agent comprises the cast iron.
 5. A method of claim1 wherein the reducing agent is at least one species selected from thegroup consisting of the iron-silicon alloy, a titanium-silicon alloy, atitanium-aluminum alloy, a zinc-aluminum alloy, a manganese-magnesiumalloy, an aluminum-zinc-calcium alloy, an aluminum-tin alloy, analuminum-silicon alloy, a magnesium-manganese alloy and acalcium-silicon alloy.
 6. A method of claim 1 wherein the reducing agentis a water soluble compound.
 7. A method of claim 6 wherein the reducingagent is an organic acid or derivative thereof, hypophosphorous acid orderivative thereof, or a sulfide salt.
 8. A method of claim 1 whereinthe reducing agent is a powder having a diameter up to 500 μm.
 9. Amethod of claim 1 wherein the contaminated matter has a water content ofat least 25 percent by weight.
 10. A method of claim 1, furthercomprising the step of maintaining the contaminated matter in a pHranging from 4.5 to 9.0 subsequent to the adding step.
 11. A method ofclaim 1, further comprising the step of maintaining the contaminatedmatter in a pH ranging from 4.5 to 9.0 under a reducing atmospheresubsequent to the adding step.
 12. A method of claim 1, furthercomprising the steps of adding an organic compost, a compostable organicmaterial, a waste water containing organic matter or a waste containingorganic matter to the contaminated matter and mixing thereof.
 13. Amethod for purifying matter contaminated with a halogenated organiccompound, which method comprises the step of: adding a reducing agent tothe contaminated matter, the reducing agent having a standard electrodepotential ranging from 130 mV to −2400 mV at 25° C. with respect to thestandard hydrogen electrode, the reducing agent is at least one speciesselected from the group consisting of reduced iron, cast iron, aniron-silicon alloy, a titanium alloy, a zinc alloy, a manganese alloy,an aluminum alloy, a magnesium alloy, a calcium alloy, and a watersoluble compound.
 14. A method of claim 13 wherein the reducing agenthas the standard electrode potential ranging from −445 mV to −2400 mV at25° C. with respect to the standard hydrogen electrode, and the reducingagent is at least one species selected from the group consisting of theiron-silicon alloy, the titanium alloy, the zinc alloy, the manganesealloy, the aluminum alloy, the magnesium alloy, and the calcium alloy.15. A method of claim 14 wherein the contaminated matter comprises 0.1 gto 100 g of an iron compound based on 1 kg of a dry weight of thecontaminated matter.
 16. A method of claim 14 wherein the contaminatedmatter comprises 1 g to 100 g of an iron compound based on 1 kg of a dryweight of the contaminated matter, and the iron compound comprises ironhydroxide (Fe(OH)₃) or triiron tetraoxide (Fe₃O₄).
 17. A method of claim15 wherein the reducing agent is at least one species selected from thegroup consisting of the iron-silicon alloy, titanium-silicon alloy,titanium-aluminum alloy, zinc-aluminum alloy, manganese-magnesium alloy,aluminum-zinc-calcium alloy, aluminum-tin alloy, aluminum-silicon alloy,magnesium-manganese alloy and calcium-silicon alloy.
 18. A method ofclaim 13 wherein the reducing agent is a water soluble compound.
 19. Amethod of claim 18 wherein the reducing agent is an organic acid orderivative thereof, hypophosphorous acid or derivative thereof, or asulfide salt.
 20. A method of claim 13 wherein the reducing agent is apowder having a diameter up to 500 μm.
 21. A method for purifying mattercontaminated with a halogenated organic compound, which method comprisesthe step of: adding a reducing agent and a nutritional source for aheterotrophic anaerobic microorganism to the contaminated matter, thereducing agent having a standard electrode potential ranging from 130 mVto −2400 mV at 25° C. with respect to the standard hydrogen electrode,the nutritional source containing an organic carbon and 20 to 50 percentby weight, based on the organic carbon, of an oxidized form of nitrogen.22. A method of claim 21 wherein the nutritional source contains 20 to30 percent by weight, based on the organic carbon, of the oxidized formof nitrogen.
 23. A method of claim 21 wherein the organic carbon issupplied as a water soluble organic carbon source.
 24. A method of claim21 wherein the reducing agent is a metal having a standard electrodepotential ranging from −400 mV to −2400 mV at 25° C. with respect to thestandard hydrogen electrode.
 25. A method of claim 21 wherein thereducing agent is at least one species selected from the groupconsisting of reduced iron, cast iron, an iron-silicon alloy, a titaniumalloy, a zinc alloy, a manganese alloy, an aluminum alloy, a magnesiumalloy, a calcium alloy and a water soluble compound.
 26. A method ofclaim 21 wherein the reducing agent is a water soluble compound.
 27. Amethod of claim 21 wherein the reducing agent is a powder having adiameter up to 500 μm.
 28. A method of purifying a contaminated mattercontaining a halogenated compound and a solid matter, which methodcomprises the step of: mixing a reducing agent and a nutritional liquidcontaining a nutritional source for a heterotrophic anaerobicmicroorganism and water with the contaminated matter, the reducing agenthaving a standard electrode potential ranging from 130 mV to −2400 mV at25° C. with respect to the standard hydrogen electrode, wherein themixing step including a step of adjusting the contaminated matter at pHranging from 4.5 to 9.0; and keeping the mixture in a condition that airhardly penetrates through a matrix.
 29. A method of claim 28 wherein thereducing agent is in a powder form and wherein the nutritional liquid isadded to the contaminated matter and mixed thereof, and then thereducing agent is added to the resultant mixture and further mixedthereof.
 30. A method of claim 28 wherein the reducing agent is a powderhaving a diameter up to 500 μm.
 31. A method of claim 28 wherein thereducing agent is at least one species selected from the groupconsisting of reduced iron, cast iron, iron-silicon alloy, titaniumalloy, zinc alloy, manganese alloy, aluminum alloy, magnesium alloy andcalcium alloy.
 32. A method of claim 28 wherein 1 to 10 percent byvolume, based on the contaminated matter, of the nutritional liquid isadded to the contaminated matter and mixed thereof as a first step; andthen an amount larger than the amount of the first step of thenutritional liquid is added to the contaminated matter and mixed thereofas a second step.
 33. A method of claim 28 wherein: 1 to 5 percent byvolume, based on the contaminated matter, of the nutritional liquid isadded to the contaminated matter and mixed thereof as a first step; thenutritional liquid is added to the contaminated matter and mixed thereofas a second step wherein a sum of the nutritional liquids added in thefirst step and the second step amounts 5 to 10 percent by volume, basedon the contaminated matter, of the contaminated liquid; and thenutritional liquid is added to the contaminated matter and mixed thereofas a third step wherein an amount of the nutritional liquid added in thethird step is more than an amount of the nutritional liquid added ineither the first step or the second step.
 34. A method of claim 28wherein the reducing agent is a water soluble compound, and the reducingagent is dissolved in the nutritional liquid.
 35. A method of claim 28wherein in the keeping step the mixture is kept at a temperature rangingfrom 17° C. to 60° C. for at least an initial three days.